curs geoternal in limba engleza

7/30/2019 curs geoternal in limba engleza

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Geothermal Energy

Written by Shota Nozadze


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Introduction 2

1. Dry rock and hot aquifer analysis .. 5

2. Environmental aspects of using thermal waters. 12

3. Methods and systems of increasing energy efficiency

of complex heat-cold supply with the use

of geothermal sources 15

Conclusions 43

References. 44

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IntroductionThe inner core of the earth reaches a maximum temperature of about 4000C. Heat

passes out through the solid submarine and land surface mostly by conduction-geothermal heat and occasionally by active convective currents of molten magma orheated water. The average geothermal heat flow at the earths surface is only

0.06W/m2, with a temperature gradient of less than 30C/km. this continuous heatcurrent is trivial compared with other renewable supplies in the above surfaceenvironment that will in total average about 500 W/m2. However at certain specificlocations increased temperature gradients occur, indicating significant geothermalresources. These may be harnessed over areas of the order of square kilometers anddebts 5km at flaxes of 10-20 W/m2 to produce 100 MW (thermal)/km2 incommercial supplies for at least 20 years of operation.

Geothermal heat is generally of low quality and is best used directly for building orprocess heat at about 50 to 70C or for preheating of conventional high temperatureenergy supplies. Such supplies are established in several parts of the world and manymore projects are planned. Occasionally geothermal heat is available at temperaturesabove 150C, so electrical power production can be contemplated. Several importantgeothermal power complexes are fully established especially in Italy, New Zeelandand in USA.

It is common to use ground heat as the input to a heat pump. Although this is strictly ageothermal source such systems will not be included in this course. In general,renewable energy is defined as currents of energy occurring naturally in theenvironment. By this definition some sources of geothermal energy can be classed asrenewable because the energy would otherwise be dissipated in the environment, e.g.

from hot springs of geysers. In other geothermal sites, however, the current of heat isincreased artificially (e.g. by fracturing and actively cooling hot rocks or by drillinginto hot aquifers.), and so the supply is not renewable at the extraction rate on a longtime scale. Such finite supplies are included in this course only because they areusually included with other alternative supplies. However the process for extractingand using geothermal power are more akin to those for centralized fossil fuels than thedispersed renewable supplies of the natural environment.

Geophysics

A section through the earth is shown in fig. 1.1 heat transfer from the semi fluidmantle maintains a temperature difference across the relatively thin crust of 1000C,

and a mean temperature gradient of 30C/km. the crust solid material has a meandensity 2700kg/m2 specific heat capacity 1000J/kg*k and thermal conductivity2W/m*k. Therefore the average geothermal flux is -0.06W/m

2 and 10 20 J7km2 ofheat is stored in the crust above the surface temperature. If just 0.1% of this heat wasremoved in 30 years the heat power available would be 100MW/km2. Thesecalculations give the order of magnitude of the quantities involved and show thatgeothermal sources are a large potential energy supply.

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Heat passes from the crust by1. Natural cooling and the friction from the core.2. Radioactive decay of elements such as uranium and thorium.

3. Chemical reactions.The time constant for of such processes over the whole earth are so long that it is not

possible to know whether the earth temperature is presently increasing or decreasing.The radio active elements are consecrated in the crust by fractional recrystallizationfrom molten material, and are particularly pronounced in granite. However the

production of heat by radioactivity or chemical action is only significant over millionsof years. And the use of geothermal heat usually relies on draining heart stored in thethermal capacity of solid material and the water in the crust.Through uniform material with heat flowing outwards from the mantle there will be aconstant temperature gradient if conduction is the only heat transfer mechanism. Thetemperature gradient is high in purely conducting strata and low in regions ofincreased heat transfer were convection occurs usually by water. If radioactive oreexothermic chemical heat sources occur there will be anomalous temperaturegradients.

The earths crust consists of large plates.At the plate boundaries there is activeconvective thermal contact with the mantle, evidenced by seismic activity, volcanoes,geysers, fumaroles and hot springs. The geothermal energy potential of these regionsis very great, owing to increase temperature gradients (to 100C/km) and to activerelease of water as steam or superheated liquid, often at considerable pressure whentapped by drilling.

Moderate increases in temperature gradient to 50C/km occur in localized regionsaway from plate boundaries, owing to anomalies in crust composition and structure.Heat may be increased from such regions naturally by deep penetration of water inaquifers and subsequent convective water flow. The resulting hot springs, withincreased concentrations of dissolved chemicals, are often famous at health spas.Deep aquifers can be tapped by drilling to become sources of heat at temperaturesfrom 50 to 200C. If the anomaly s associated with material of low thermalconductivity, i.e. dry rock, then a high temperature gradient occurs with a relatedincrease in stored heat.

Geothermal information has been obtained from mining, oil exploration andgeological surveys. Only since about 1975 has there been a determined effort to

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obtain direct geothermal information, and now at least 80 countries have activegeothermal surveying programs. The most important parameter is temperaturegradient, and accurate measurements depend on leaving the drill hole undisturbed sothat temperature equilibrium is re-established after drilling. Deep drilled survey wellscommonly reach depths of 6km, and the technology is available to drill to 15km. the

principal components of a geothermal energy plant are the boreholes, and so heatextraction from depths to 15km can also be contemplated.

There are three classes of geothermal region:1. hyperthermal temperature gradient > 80C/km. these regions are

usually on tectonic plate boundaries. The first such region to be tapped forelectricity generation was in 1904 at Larderello in Tuscany, Italy. Nearly allgeothermal power stations are in such areas.

2. semithermal temperature gradient 40C/km to 80C/km. such regionsare associated generally with anomalies away from plate boundaries. Heatextraction is from harnessing natural aquifers or fracturing dry rock. A well-

known example is the geothermal district heating system for houses in Paris.3. Normal temperature gradient < 40C/km. these remaining regions are

associated with average geothermal conductive heat flow at 0.06W/m2. It isunlikely that these areas can ever supply heat at competitive to present finite,or future renewable, supplies.

In each class it is, in principle, possible for heat to be obtained by:1. Natural hydrothermal circulation, in which water percolates to deep

aquifers to be heated to dry steam, vapor/liquid mixtures, or hot water.Emissions of each type can be observed in nature. If pressure increases bysteam formation by deep levels, spectacular geysers may occur, as theGeysers near Sacramento in California and in the Wairakei area nearRotorua in New Zeeland. Note, however, that liquid water is ejected, and notsteam.

2. Hot igneous systems associated with heat from semimolten magma thatsolidifies to lava. The first power plant using this source was the 3MW(e)station in Hawaii, completed in 1982.

3. dry rock fracturing Poorly conducting dry rock, e.g. granite, stores heatover millions of years with a subsequent increase in temperature. Artificialfracturing from boreholes enables water to be pumped through the rock toextract the heat.

In practice geothermal energy plants in hyperthermal regions are associated withnatural hydrothermal systems; in semithermal regions both hydrothermal and hot rockextraction is developed; and normal areas have too small a temperature gradient forcommercial interest.

1. Dry rock and hot aquifer analysis

Dry rock

We consider a large mass of dry material extending from near the earths surface todeep inside the crust (fig.1.3). The rock has density pr, specific heat capacity crand

cross-section A. with uniform material and no convection, there will be a linearincrease of temperature with depth. Ifzincreases downward from the surface at z=0,

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GzTzdz

dTTT 00 (1.1)

Let the minimum useful temperature be T1 at dept z1,so

;101 GzTT G

TTz 011

(1.2)

The useful heat EG at the temperature T grater than T1 in an element of thickness zG at

depth z is

)()( 1TTcAE rzr GUG ( ArU )() 1zzGcrz G (1.3)

The total useful heat content of the rock to depth z2 becomes

2/)(

)2/(

)(

2

12

1

2

10

2

1

2

1

zzGAc

zzzGAc

dzzzGAcE

rr

z

zrr

rr

z

zz

U

U

U

(1.4)

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Alternatively , let the average aveilable temperature greater than T1 be

2/)(2/)( 1212 zzGTT T (1.5)

Then TrCE 0

Where Cris the thermal capacity of the rock between z1 and z2

)( 12 zzAcC rrr U (1.6)

So as (1.4),

)( 210 zzGAcE rr U (1.7)

Assume heat is extracted from the rock uniformly in proportion to the temperature

greater than T1 by a flow of water. Volume flow rateV , density wU , specific heat

capacity cw.The water will be heated through a temperature difference of in the nearperfect heat exchange proses

Thus

dt

d

CcV rwwT

TU

(1.8)

dtCr

cVd wwU

T

T.

W

dt(1.9)

and

WTT /0te

(1.10)

The useful heat content TrCE . So

W/0

teEE (1.11)

And

W

W

/0 teE

dt

dE (1.12)

Where the time constant W is given by

ww

rr

ww

r

cV

zzAc

cV

C

U

U

UW

)( 12

(1.13)

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Hot aquifers

In a hot aquifer the resources lies within a layer of water deep beneath the groundsurface (fig. 1.4). We assume that the thickness of the aquifer is ( h) is much less than

the depth (z2) below ground level, and that consequently the water is all attemperature T2. The fraction of the aquifer containing water is the porosity p`, withthe remaining space of rock of density pr. The minimum useful temperature is T1. Thecharacteristics of the resource are calculated similarly to those for dry rock.

GzT

dz

dtTT 002 (1.14)

)( 120 TTC

A

Ea (1.15)

Where

hpcpC wwa ))1(( cc U (1.16)

As with (1.8) onwards, we calculate the removal of heat by water volume flow rate Vat

T , aboveT1

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dt

dCcV aww

TTU (1.17)

So

)/exp(0 atEE W (1.18)

)/exp()/( 0 aa tEdt

dEWW (1.19)

and

ww

rrww

ww

aa

cV

hcpcp

cV

C

U

UU

UW

))1(( cc (1.20)

Harnessing geothermal resourcesGeothermal power arises from heat sources having a great range of temperature andlocal peculiarities. In general, available temperatures are much less than fromfurnaces, and although much energy is accessible the thermodynamic quality is low.The sources share many similarities with industrial waste heat processes and oceanthermal energy conversion.

Matching supply and demand

With the geothermal source it is always sensible to attempt electricity generation sincethis is a value product, and the rejected heat can be used in a combined heat and

power mode. Electricity can be distributed in a widely dispersed grid and integrateswith other national power supplies. Nevertheless the energy demand for heat at 300C, and unattractive if


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The total amount of heat extracted from a geothermal source can be increased byreinjecting the partially cooled water from the above ground heat exchanger. This hasthe extra advantage of disposing of this water, which may have about 25kg/m3 ofsolute and be a substantial pollutant. Nevertheless a substantial extra cost is incurred.

Extraction techniquesThe most successful geothermal projects have boreholes sunk into natural waterchannels in hyperthermal regions (fig. 1.5). This is the method used at the Geysers,California, and Wairakei, New Zeeland, were there is a considerable overpressure inthe boreholes. Similar methods are used for extraction from hot aquifers insemithermal regions, where natural convection can be established from the boreholewithout any extra pumping.Recent interest has concentrated on extraction from dry hot rocks since these may bemore extensive than wet aquifer sources. The leading development group (at the LosAlamos Scientific Laboratory, USA) has pioneered methods of fracturing the rockwith pressurized cold water around the end of the injection borehole (fig. 1.6). After

the initial fracturing, water is pumped down the injection bore to percolate through thehot rock at depths of5km and temperatures 250C before returning throughshallower return pipes. Complex arrays of injection and return boreholes might enablegigawatt supplies of heat to be obtained.

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Thermal water is one of the natural forces destined in the near future to play animportant role in development of the Moldova energy system and the nationaleconomy.

Moldova is abundant in natural thermal waters and has a long history and tradition oftheir utilization. Currently, about 100 natural (springs) and artificial (wells) watermanifestations with temperature 30 C 80 C have been registered in Moldova. Theirtotal discharge is about 50 000 m3/day. But their potential is far greater. It has beenestablished that the thermal water inferred resources are 250-350 million m3 perannum. The spectrum of utilization of thermal waters is quite wide. It is used inindustry, agriculture, municipal services, balneology, etc. Using modern technologyfor the development of available geothermal resources will make it possible to save2.5 million tons of equivalent fuel annually. This will be of considerable economicand ecological importance. By replacing this amount of traditional fuel by geothermalenergy, it will be possible to reduce the amount of CO2 released into the air by about

1 200 000 tons annually.

Estimations have shown that, in the majority of cases, geothermal heat is 5-6 timescheaper than all kinds of fuel and the payback period of investments is shorter.

Geothermal water resources can be used in heat supply to agricultural objects(greenhouses, farms, processing factories and plants, mushroom-growing, fish culture,etc.), hot water and heat supply to the municipal sector, the extension of the networkof health resorts, hospitals, therapeutic tourism, development of sport facility systemand health-improving complexes and other various kinds of activities where heat

plays an important role.

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2. Environmental aspects of using thermal waters

In order to use the resources of underground heat of the earth, the problems of soil-deposition and corrosion must be handled, which are quite complicated. Someresearch works were carried out with the purpose of development of such product thatwould simultaneously provide softening, decontamination (cleaning water from radonand radium), prevention of corrosion of heating systems metal parts and reduction of

process costs with the purpose of effective usage of geothermal waters. A coagulanthas been developed with following relation of components in percentage according tothe thermal water: oxalic acid 2-6 %; phosphoric acid 1-3 %; ammonium hydroxyl

4-6 %; gypsum 0,1-0,2 %; the rest is water [8]. The coagulant permits to softengeothermal water with high salt content to zero. The coagulant is added to the water inthe amount of 0,3-0,5% of the processed water; it also removes radon and radium,

which deactivates the water and prevents the corrosion of metal pipes. The technologyconsists in adding the coagulant to the processed geothermal water, mixing, settling inthe depositing tank and after passing the appropriate filter supplying the thermal waterto the consumer. The specified method gives considerable economical effect. Forexample if softening of 1 ton of geothermal water by known methods of softeningcosts $3, then, according to the specified method, it will cost $0,80 (year) [35].Geothermal waters, which are suitable for drinking and whose mineralization does notexceed 1,2 g/l, might be used by direct schemes. If geothermal waters do not satisfythe requirements mentioned above but possess sufficiently high thermal potential,they can be used in the systems of heat-cold supply through intermediate heatexchangers.

As geothermal waters often have high mineralization and also are aggressive, it isnecessary to elaborate devices that will permit to bring geothermal waters to therequired conditions. On fig. 2.1 [3] is shown the basic diagram of a degassing unit; onfig. 2.2 is given the scheme of using heat of highly mineralized geothermal waters.Geothermal water (fig. 2.1) is supplied from the bore to the degasator (1), wheredegasation takes place; gases from the water are being blown out and directed to thewet gasholder (5) by the fan (4); degassed water, passing through the buffer tank (2) isdirected to the consumer (3).

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On fig. 2.2 [1] highly mineralized geothermal water is supplied from the bore (3), issprayed and passes a nozzle of the degasator (1). Meanwhile, warm air from below is

blown by the ventilator (4) and minerals remain on the nozzle; the water begins toaccumulate and, already discharged, is supplied to the consumer; the heat of highlymineralized geothermal water is used to heat fresh water, which is supplied from thereservoir (2) and is directed according to its purpose.

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The offered method of using highly mineralized thermal waters permits to utilize theheat of these waters effectively for heating extraction waters, preventing salts andaggressive elements from being transferred to the heat exchanging surfaces. In thatway, implementation of suggested measures creates certain prerequisites for wide useof thermal waters in various fields of economy. Wide application of geothermalwaters in heat-cold supply systems is one of the effective measures for saving fossil

fuel. Especially high saving of fuel-energy resources are present in the fields of heatsupply of residential, public and industrial buildings, also in low temperature (below100 C) technological processes of various fields of economy.Main directions and problems of scientific and technological advance in usinggeothermal resources are: improvement of operating schemes of geothermal heatsupply, considering their specific features; maximization of using heat potential ofthermal waters by multi-step utilization of waters by various consumers, building oflarge water reservoirs on the basis of discharged thermal waters for fish farming;creation of small hothouses along the heating hot-water systems for significantreduction of thermal water heat losses at their transportation; all possible widening ofhigh- performance and economically profitable geothermal heating of greenhouses;

increasing scales of using geothermal waters as heat carriers in heat-pump plants.

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3. Methods and systems of increasing energy efficiency of complex

heat-cold supply with the use of geothermal sources

The heat-cold supply is fulfilled using the individual, centralized and mixed systems.Each heat-cold supply system has its peculiarities that depend on the type of the heatsource (cogeneration or trigeneration plants, heating plant, individual boilers,compressive or absorptive cooling systems) and the type of heat-cold carrier.According to the research, the efficiency increase of the heat-cold supply will be theresult of development and application of complex heat-cold supply systems. One ofthe important aspect of the energy system development of an industrial unit, region,and the country as a whole is the choice of optimal heat-cold supply schemes. Thechange of heat-cold supply schemes often changes the type of energy resources used,environmental impact and economy of the system. With the increased concern

towards environmental problems, the limit of fossil fuels and their price increase theenergy systems tend to utilize more renewable sources.

The feasibility of using geothermal resources mainly depends on the followingfactors: thermal potential (temperature), potential and possible-to-use reserves, depthof bedding and pressure, chemical composition of the water, geographical placementof water sources, the level of economical development of the region, the availabilityof other kinds of energy sources, etc. The consumption of energy resources intraditional heat-cold supply systems is proportional to the demand, while thegeothermal bore with the same output and potential might turn out to be a completelydifferent system where the customers should use the energy available during thewhole year. In this way, it is necessary to develop new schemes of complex usage ofgeothermal waters, particularly the heating systems, air conditioning, hot watersupply, generation of artificial cold for storage of vegetables and fruits, the heatsupply to greenhouses, the ground heating, etc., which would increase the energyefficiency of geothermal water usage.

For the quantitative characteristics of energy efficiency of geothermal heat-supplysystems Lokshin [20] introduced the coefficient of efficiency of geothermal heat-supply geoth, which is the relation of the bore heat actually used during the year tothe total amount of the heat, which could be gained, calculated by taking into accounta certain return temperature.

)1(max t

year

real

year

geoth izQ

QD[K

(3.1)

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where = (tw.t - 15)850010-34,19 - amount of the heat gained from 1 ton/hrdesign output, GJ/year; tw.t - wellhead temperature of the geothermal water, ; 8500

conditional number of hours used in maximal load of the sample consumer;Q

-real annual amount of heat, gained from 1 ton/hr design output of geothermal waterused by the real consumer GJ; i and z qualities of relative abrasion of overfalltemperature and usage of the maximal load. - quality of relational increase of designoutput of the bore in comparison with the heat supply of the sample consumercharacterizing the connection between the hydrodynamic regime of the water-bearinglayer and factual selection of geothermal waters. t - portion of the peak heating inannual thermal balance of the geothermal heat supply system.

max

yearQ

real

year

The value of i is defined by the formula:

15.

tw

or

t

tt

i(3.2)

where tr and to are the design temperatures of the heat carrier, which are entering theconsumer, and the return water, .

Quality of using the maximum load Z for heating and ventilation compared to the

sample consumers is calculated by the formula:

8500averseasmZ

W

(3.3)

where seasW

- duration of heating season expressed in hours; maver - average-heating

coefficient of heat outputdes

outin

aver

outinaver

tt

ttm

aver

out

; tin - the air temperature in buildings, ,

- design outdoor temperature,t

- average outdoor temperature for the workperiod of heating and ventilation, .

des

outt

It should be mentioned, that the coefficient geothK

does not provide the qualitativecharacteristic of geothermal heat-cold supply and by that does not show the priorities

of geothermal heat supply in comparison with the traditional ones. The improvementof technical and economic indicators, also the development of methods and systems

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of increasing energy efficiency of the national economy complex heat-cold supplybranches with the use of geothermal waters requires the development of varioustechnical facilities and aggregates. The heat exchangers, heat pump plants, absorptiverefrigeration machines, etc. are the examples. Therefore, to evaluate the used energyof geothermal waters, it is appropriate to make use of general thermodynamic

methods of the analysis with exegetic method, permitting to evaluate the energyefficiency according to the second law of thermodynamics.

3.1. Methods of comparing different sources of heat-cold supply systems according

to the exergy efficiency

Exergy is the maximum quantity of work obtainable when some matter is brought to astate of thermodynamic equilibrium with the common components of the naturalsurroundings by means of reversible processes, involving interaction only with the

above mentioned components of nature [34]. The condition of thermodynamicequilibrium with the surroundings should be understood as the condition of countingout (zero level) on calculating of the convenience of the geothermal heat carrier. Forinstance, the thermal energy is not equal to its amount in contrast to the mechanicaland electrical energy, where the amount of energy and exergy are equal, i.e. electricand mechanic energy might be completely turned into another kind of energy [7].Therefore, exactly the exergetic method is the most convenient instrument whencomparing the geothermal energy to other forms of energy. The most importantindicator along with the initial energy is the exergetic efficiency, defined by therelation of effectively used energy to the maximum possible.

The exergetic efficiency of heat supply from the boiler plant can be calculated in thefollowing way [7].

f

hphwshphwsaverhbhs

exeB

eeme

WWK

8500)( '''

(3.4)

where ehb exergy of heat carrier in heating systems at estimated thermal load;

maver - average-heating coefficient of the heat output; hpW

- the duration of the

heating period; - exergy of the water, consumed on the hot water supplycorrespondingly in winter and summer; B, ef - the fuel consumption on heat supplyand its specific exergy.

''' , hwshws ee

The meaning of is defined as the exergy of the heat flow [37] at thetemperature of the surroundings in winter Tsurr=278 K, and in summer Tsurr=288 K.It is obvious, that ehb=Qhb , where Qhb - calculated thermal load; - exergetic

temperature function for the temperature of the heated building; = Q ,

''' ,, hwshwshb eee

'hwse 'hws

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''

hwse

hs

exK

= whereQ

,Q

- thermal load on the hot water supply correspondinglyin winter and summer. Fig. 2.1 [13] shows the dependence of the exergetic efficiency

of heat supply on boiler plant efficiency

''

hwsQ'

hws

''

hws

boilK . The analysis of this dependenceshows that even if the boiler plant efficiency equals to 0,85, exergetic efficiency of

heat and hot water supply does not exceed 0,35.

E'

bed

net

E

Egex

K

At the geothermal heat supply the distribution of the exergy of the bedded geothermalwater can be seen in three different versions. In the first version the definite exergy ofthe thermal water is lost with the evacuation of water. In the second version, after

being used, the geothermal water is pumped into the bed, which partly saves the waterexergy, but for pumping-in the water the electrical energy is spent. Therefore, whendefining the energy consumption of the pumping-in from the point of view of savingof the exergy, it is necessary to compare the exergy of the pumped in geothermalwater to the electrical energy used by the pump. In the third version, exergy gained

from the geothermal water is completely spent by the consumer. On the whole, exergybalance, when using the geothermal waters for heat supplying, can be put down thisway:

resnetbed ENEE (3.5)

where Ebed - exergy of the bedded geothermal water; Enet - net exergy used ofthe geothermal water; E - total losses of the exergy in the bore, heating network

pipes, heat exchangers and at the evacuation of water; N - total consumption of theelectrical energy on transporting of the thermal water in the heating system; Eres - theresidual exergy of the geothermal water.

Exergy efficiency of the geothermal heat supply [13] defined by the relation

will be the highest in the third version and, at the sufficient excess

pressure at the wellhead, which is excluding the spending on the electric energy, andthe bores located near the consumer, the efficiency will tend to one. The composition

and the

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LauxLhex

Ldisch

Fig.3.2 Exergetic diagram for geothermal heat

supply

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analysis of the exergy balance at the geothermal heat supplying permit to evaluate thespending of the exergy in the process of the heat supply. As an illustration theexergetic graph for the geothermal heat supplying [13] is presented (fig. 3.2). Assume,that the temperature of the bedded water is 85 , the temperature at the inputterminal of the heating device is 80 and the temperature of the evacuation is 30 .

The analysis of the graph shows that the considerable losses of the exergy might occurin the bore shaft as well as in the pipes network.

At the pure geothermal heat supply, the exergic efficiency [13] is defined as:

> @ > @ hwsurrbedsurrsurrbedhwhsurrbedsurrsurrbedh

hhwhhwhh

bed

netg

exSSThhGSSThhG

eeme

E

E

WW

WWWK

'''

'''8500

(3.6)

Here is the enthalpy of the bedded geothermal water and the enthalpycorresponding to the temperature of the surroundings in winter and summer;

- entropy of the bedded geothermal water and the surroundings;

- geothermal water mass flow for heating, hot water supply,

correspondingly in winter and summer;T

- temperature of the surroundings

in winter and summer.

',,surrsurrbed

hhh

surrS

''' , hwhw G

bedS ,

,h GG

',surrsurrT

The graph showing the dependence of the exergy efficiency on the evacuation

temperature of the geothermal water, after being used in the heat supply system (fig.2.3)[7], is constructed according to the formula (2.6). The exergy efficiency of the

resistance heating is defined by the formula:

TKKcp

htel

ex

.

(3.7)

where cpK

is the exergy efficiency of the condensing plant. The graph of dependence

of

ht.el

ex

Kexergy efficiency of the resistance heating on the exergy efficiency of the

condensing plant (fig. 2.4)[7] is constructed according to the formula (3.7). As could

be seen from the graph the minimal value of the exergy efficiency equals 0, 01.

Exergic efficiency of the VCHPS (Vapour Compression Heat Pump System) can be

represented as following [38]:

evevbr

vhgwvhgwvhvh

br

netVCHPS

exQW

eeme

E

E

T

WWWK

8500'''

(3.8)

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HereW

- the electrical energy spent in the Heat Pump System;Q

- the amount of

the low-grade heat brought to the Heat Pump evaporator.

br ev

evT

- exergetic temperaturefunction applied from the low-grade heat to the working fluid in the evaporator.

The formula for the absorptive Heat Pump can be written in the same way:

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evevbrbr

vhgwvhgwvhvh

br

netAHP

exQQ

eeme

E

E

TT

WWWK

8500'''

(3.9)

Here - amount of the heat brought into the Absorptive Heat Pump (AHP)

generator;

brQ

brT - the exergic temperature function applied to the heat brought to theAHP generator. The formulas (2.8) (2.9) permit the VCHP and AHP to be compared

by energy efficiency.

The graphs, showing the dependence of the VCHP and the AHP exergy efficiency onthe temperatures of the heated heat carrier, heating water in the AHP generator andthe low-grade water in the evaporators (fig. 2.5), are constructed according to theformulas (2.8) and (2.9). As shown on the graph, the energy efficiency of the VCHPis greater than of the AHP, which is the result of a higher degree of the

thermodynamic performance of the condensing plant over the boiler plant, also thehigher degree of the transmission facilities over the heating network. On fig. 2.6 canbe seen the exergetic balances of the VCHP and AHP, which permit to analyze theloss of the exergy in their main elements and develop the recommendations for theirimprovement.

The fuel consumption on a unit basis for generation of heat in VCHP, AHP, electricboiler plants, boiler plants that run on fossil fuel and in the combined heat and powerplants, is defined by the formulas:

VCptlcp

wl

VCHP COPQb 1

1

KK (3.10)

A

tnb

w

l

AHPSCOPQ

b1

1

KK(3.11)

ptlcp

w

l

elQ

bKK

1

(3.12)

tnb

w

l

bQ

bKK

1

(3.13)

tn

CHP

c

w

l

CHPQ

bKK

1

(3.14)

On the fig. 3.7 is shown the dependence of fuel consumption in VCHP, AHP andboiler and the temperature of the heat carrier thc. The dashed lines on the graph show

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the areas, which display the unit discharge of the fuel. As shown on the fig. 3.7, thedependence of the unit discharge of the fuel for getting the heat in the heat pumpsystems on the final temperature of the heated heat carrier (at other parameters beingconstant) is similar to the dependence for steam extraction of the combined heat and

power plant.

The unit discharge of fuel for generation of heat in the boiler plants show differentnature. The thermal efficiency of boilers, when increasing the temperature of the heatcarrier, is reduced insignificantly. Thus, the increase of t causes a slight increase of

bboil on the graph.

In heat pumps the upper level of the temperature can be controlled, by the possibilityof choosing of the thermodynamic cycle; it exceeds the needed temperature of the

heat carrier only by several degrees. The process of getting the needed

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temperature does not go top-down, as in boiler plants, but it goes bottom-up by usingthe reverse thermodynamic cycle of the natural low-grade heat on the bottom level.

The bVCHP on the graph (fig. 3.7) uninterruptedly goes down because of increasingtemperatures of low-grade heat carrier and at 95-100C it crosses with bCHP [38].Consequently at these temperatures of the heated water and their corresponding initialtemperatures of a low-grade heat carrier (35-45C) VCHP becomes economicallyequal to combined heat and power plant in the energy consumption.

The lowest energy efficiency is characteristic to electric boilers. It changes in thetemperature interval 60 - 100C within the limits: bel = 100130 kg/GJ (notshown on fig 3.7 because of the scale). Thus, for heat supply purposes, the methods ofenergetic comparison have determined the VCHP to be energetically more beneficial

than AHP. Competitiveness of AHP goes down even more because of the need tobring the heat carrier of comparatively high parameters hot water of 110-130C or

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vapour under the pressure of 1,2 2,4 bar. Nevertheless, as AHP are more effectivethan boiler plants, they can be used in certain conditions, when cheap heat isavailable.

Considered sources of heat supply are arranged in the order of increasing energyefficiency: electric boiler plants, boiler plants that run on fossil fuel, AHP, VCHP,combined heat and power plant. Considering geothermal heat supply some questionsarise: how effective it is and at what level of exergetic efficiency of geothermal heatsupply the initial fuel consumption is decreased. As an example lets compare the heatsupply from the boiler plants on an fossil fuel with different thermal efficiency. Theresults of this comparison are shown on the fig. 3.8 [38]. The analysis of dependencesof the graphs shown on the fig. 2.8 permits to define the minimal meaning of an

exergetic efficiency of geothermal heat supply . For instance, = 0,5,g

exKboil

tKg

exK

=0,11 is the lowest level for the initial energy to be economized and consequently the

scheme of geothermal heat supply, in this case, must be chosen so thatg

exK is morethan 0,11.

3.2 Development of systems of complex heatcold supply of industrial consumers

with the use of geothermal sources

The main peculiar features of heatcold supply consumers of the agroindustrialcomplex (AIC) are: wide range of technological schemes of farm production,

connected to the heatcold consumption depending on the power of an enterprise andtheir specializations; complexity and individual character of fuel and energy supply ofthe AIC objects which usually have several heat and cold consumers of different

potentials (thermotreatment of raw materials, lowtemperature storage of rawmaterials and products, technological air conditioning, etc.); considerable diurnal andseasonal oscillation of heatcold discharge by the consumers, appreciably exceedingthese oscillations in other fields of national economy; considerable dispersion andcomparably small power of separate heatcold consumers.

Accounting of specifics of heatcold supply of the AIC consumers permits to group

them. There are five characteristic groups of heatcold consumers, which significantlydiffer not only in their magnitude, but in heatcold consumption regimes as well [29].Below there are the characteristics of the consumers and the methods of building ofcomplex heatcold supply systems with the use of geothermal sources.

a) Thermal and greenhouse economy characterized by huge heat consumption(power inputs make up 21% of the manufacturing cost), which mainly dependson plant growing and meteorological conditions. In greenhouses there aresignificant electric power for additional lighting in mornings and evenings,which in fact are not used at night. On average, thermal and electric energy

consumption on 1 ton of product is 131,6 GJ and 65 kWh respectively [10,25].

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b) Vegetable and milk state farms and animalraising farms are characterized bycomplex structures of heat balance and huge variation of heatcoldconsumption regimes. Heat is mainly used for heating and ventilation, also fortechnological needs, such as hot water supply and forage preparation, whichare almost permanent during the year and cyclic during the day, heating andventilation belong to the seasonal thermal load. Cold storage of products andair conditioning systems also belong to the seasonal consumers.

It should be indicated that at slight regulation of the indoor climate in theanimalraising farms there could be a significant economical effect. On thesefarms can use also quite effectively the secondary energy resources, the milkheat and the heat of ventilation discharge. If the animal maintenanceconditions and veterinarysanitary standards on these farms and complexes

are poor, then the productivity and the illness tolerance of these animals aredecreased; growth and development of young animals are slowed down. Forexample, keeping animals in cold, damp, poorly ventilated buildings leads todecrease in their productivity by 20 40%, increase in their food expenses by12 35% and increase in morbidity 2 3 times. The air temperature is themost essential, determining factor of the indoor climate in animalraising

buildings. According to the researches made in Hungary and the USA, [39]forage consumption at growing and fattening of pigs in nonheated buildingsincreases by 25 30%, daily increment in pigs mass decreases by 12 38%.The optimal temperature of the air in the farm buildings is 15 20 C [39].

Cattle are less sensitive to low temperatures than pigs. However, thetemperature reduction below the critical level, in this species, leads to increasein metabolism by 2 3% for each degree of reduction, overhead of forage by15 50% and more, decrease in dairy production and mass increment by 15 30%; this is inexpedient from economical point of view.

Creation of the optimal indoor climate in animal-raising buildings is done byventilation. Unless the air in animal-raising buildings is exchanged withexternal air, it will soon obtain harmful components. Water vapours, gases,

dust and microorganisms will gather in it. In that way, organization of optimalsystems of influx-and-extract ventilation is the main link of rationalization ofentire animal-raising economy, and probably is determined with minimalspending by means of application of complex heat-cold supply system on the

basis of thermal waters.

c) Drying of grain, hay and agricultural production is a power-consumingprocess which usually involves the usage of high quality liquid fuel. Theactual character of the regime depends on the organization of thesetechnological processes, which are characterized by expressed seasonalexpenses of the initial energy resources. Taking into account that drying of

agricultural production mainly takes place in summer and in early autumn,

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there are possibilities of year-round, almost steady usage of geothermal heatsources.

For better preservation of the initial quality of agricultural production,including grain, new, effective methods of conservation have to be found. Oneof these methods is the usage of artificial cold, which becomes the essentialand important element in technological processes of grain processing and

partly characterizes the scientific and technical progress in the system ofbakery subcomplex of the AIC. Cooling of grain down to 15 C permits todelay the evolution of plant pests or totally eliminate them. The researchescarried out by the Kuban branch of the All-union research institute on grainand its products showed that the temperature of 6 C permits to stabilize thequality of fresh seeds of the sunflower temporarily, before drying them, also tokeep the quality of the dried seeds to be kept for up to 1 year [11]. So, usingcold for keeping and heat for processing cereal crop has a big practicalsignificance and can be complexly solved with minimal costs using the drying

and cooling systems with the use of geothermal heat sources.

d) Storage of fruit and vegetables is characterized by huge cold usage, whichmainly depends on the type of the products kept and the cooling systems.Reduction of foodstuff loss is an important condition for realizing food

programs. Several countries tend to decrease the structures of refrigerativesystems and increase the portion of vegetable products. This is explained bynew needs of nutrition hygiene. For example, fruits and vegetables coverapproximately 50% of refrigeratory systems in France [29]. Fruits and

vegetables are more sensitive to slight changes in microclimate parameters anddeteriorate faster than seed, which is caused by their big evaporatingcapability, uninterrupted release of physiological heat and increased reactionto the loss of moisture [29]. Development of reliable methods for storage ofraw vegetable materials has significant meaning. Solution to this problem can

be found by using inexpensive systems of air conditioning with liquid sorbentsusing geothermal sources and active ventilation of raw vegetable stacks.

e) Tobacco and milk factories, canning production, which simultaneously useboth, heat and cold, in existing systems of separate heat-cold supply, usuallyuse high quality liquid fuel for getting the heat. For getting cold they usecompressive refrigeratory machines.

Currently, on existing tobacco factories of Moldova withering, predrying anddrying are fulfilled using low effective heaters running on heavy oil. In thiscase, as the products of incomplete burning are mixed with the heated air, thetobacco quality decreases and in some cases, because of limited possibilities of

precise regulation of the air temperature and moisture, it leads to drying up ofa tobacco leaf, which causes the product loss. At the accepted schemes ofenergy supply it is difficult to provide the necessary temperature-moistureregime for twisting and fermentation processes of a tobacco leaf. This alsoleads to quality decreasing of the ready product.

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The character of tobacco factories is a big amount of collateral energeticresources in the form of thermal moistened air, thrown out of charging anddrying aggregates.

Dairy factories and peripheral milk-receiving stations simultaneously areconsumers of both heat and cold. For getting hot water small boiler plants orheat-generators are used, and for cooling processes refrigeratory plants areinstalled. Replacement of traditional separate systems of heat and coldgeneration by single combined process of complex heat-cold supply based ongeothermal sources permits to eliminate the atmospheric emission of waste

products of burning, saves fresh water and fuel- energy resources. Similarcomplex heat-cold supply systems using geothermal sources can besuccessfully incorporated into tinned food factories, soft drink factories,

breweries, etc.

Below are considered main methodical positions and examples of developingcomplex heat-cold supply systems using geothermal sources for the groups of

technological consumers mentioned above.

Appropriateness of using thermal energy of geothermal waters in a specific region isdefined by the following factors: energetic potential of geothermal water field,chemical composition of water, general energetic complex of a region and specifics ofits economic development. For selection of complex heat-cold supply system it isnecessary to determine the number of consumers of geothermal water in ratedconditions, which are classified by demands made by them to the potential of heatcarrier; then order of geothermal water delivery is designed, considering the inter-location of different categories of consumers and cooling level using geothermalwater; design parameters of schemes are defined and possible seasonal consumers are

chosen.

The temperature of geothermal water varies in wide ranges. Fig. 3.9 presents thelayout of geothermal waters by the temperatures and gives possible versions of usingthermal waters for heat-cold supply of technological processes, heating, hot watersupply, air conditioning, cold supply of fruit and vegetable storehouses, cold supplyfor refrigerator chambers heat supply of greenhouses, heating the ground in hotbeds.It is possible to choose the corresponding variant of complex usage of thermal water,

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based on the temperature range of geothermal

bore. As it is shown in fig. 3.10 [10], year-round consumers of geothermal water arethe systems of hot water supply and the refrigeratory plants. The seasonal consumers

are heating systems of greenhouses, air conditioning, tobacco factories, tinned foodfactories, dairy factories, drying plants of agricultural production, etc. Sequence ofconnecting various consumers to geothermal sources depends on their parameters andoperating mode. Therefore, it is necessary to develop optimal schemes of heat-coldsupply of various consumers taking into consideration the specifics of geothermalheat supply.

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Vegetable growing in the protected ground is one of the most energy-consumingbranches of agricultural production. Main way to reduce the energy inputs is todecrease the investment and fuel consumption on greenhouse heating. Cost of agreenhouse heating system depends on two main parameters: nominal thermal powerand cost for tubing. The first parameter is defined by the climate conditions of aregion; the other is defined by the construction and design of heating system. At

present there have been accumulated the experimental data characterizing thequalitative side of separate elements of heat and mass exchange processes in thesystem of ground plant and air greenhouse. As a result of processing the

experimental data the empiric formula for calculating the specific thermal load ofgreenhouses has been obtained, GJ/hr, for 1 hectare [10]:

61011,0 outinhh

ttFQ(3.15)

The area of the greenhouses, which can be connected to the geothermal heat supply,is:

outintvtvhh

tttGF 351011,0 3(3.16)

where stands for geothermal water discharge ton/hr;t

- temperature of the

geothermal water in the system of greenhouse heating; t - air temperature inside the

tvG

tv

in

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hothouse; - design temperature of the outdoor air; 35 - temperature of thegeothermal waters at the output from the heating system.

outt

The values of geothermal water discharge are shown in table 3.1 for 1 hectare ofgreenhouses at various initial temperatures of thermal water and outdoor air;according to equation 3.15

On the fig. 3.11 are shown the dependences of change in maximal total thermal loadfor 1 hectare of hothouses depending on the air temperature (a).

Table 3.1 Maximal thermal load for 1 hectare of hothouses [10]

Unit discharge of geothermal waters, m3/h hectare, at the outdoor air

temperature

Temperature

ofgeothermalwater, -16 -12 -8 -4 0 4 8 12 16

100 50,4 48,8 39,2 33,6 28,0 22,4 16,8 11,2 5,6

90 60,5 53,9 47,3 39,7 33,1 26,5 19,8 13,2 9,9

80 72,5 64,5 56,5 48,5 40,4 32,3 24,2 16,2 11,2

70 93,4 83,0 72,6 62,3 52 41,6 31,2 20,8 12,3

60 116,9 108,6 101,3 87,3 72,7 58,2 43,6 29,1 14,5

50 122,4 116,9 109,3 95,8 81,2 66,7 52,1 38,6 22,9

40 132,9 127,4 119,8 105,9 91,7 77,9 62,6 48,9 33,4

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Yearly graphs of heat discharge on the hothouses were built according to the climate

data [26]. As an example on fig. 3.12 (b) is given such graph for greenhouse-vegetable complex in the Kindgi region. As shown on fig. 3.12 (b) the number ofworking time of the greenhouses per year is approximately 4600 hours. Connectingother consumers to the geothermal sources permits to increase the number of hours ofusing the thermal potential of a bore significantly. As it was mentioned above, thecost of a greenhouse heating system is defined by its steel intensity, which depends onthe construction of this system. The minimal cost of tubing is characteristic for the airheating system using fans. But along with its technical-economical values it hasnegative sides as well from the point of view of satisfaction of agrobiologicalrequirements in the microclimate created by it. It is based on the fact that hothouse issupplied with overdried air, which leads to significant decrease in relative moisture ofthe greenhouse air. Consequently, crop capacity is reduced and even some plantdiseases are developed [9]. Therefore in the greenhouses is better to use combined

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heating systems and humidifiers. As a result, it becomes necessary to carry out specialscientific researches of perfection and optimization of the heat supply systems and air-conditioning for agricultural and industrial consumers to provide the optimalconditions of technological regime and increasing of productivity.

The creation of heat-cold supply systems using direct heat exchangers andpolyethylene heating devices running on geothermal heat carrier, to some extent,might help to solve the problems.

Fig. 3.12 [9] shows the basic diagram of combined heating system and air-conditioning of greenhouses using direct heat exchangers on the basis of geothermalwaters.

To reach the maximum efficiency in using the thermal potential of geothermal waters,it is necessary to apply the system of soil heating with the use of hollow-core panelson the basis of discharged geothermal waters. In a general complex of heating devicesof modern construction of protected ground, soil heating plays an important role. The

purpose of soil heating is to change the temperature-moisture regime of the close-to-surface layer of the soil. Depending on the quality of a plant development, variousdemands are made to the temperature of ground and greenhouse air. Only thecombination of both types of heating can provide the possibility to heat soil andgreenhouse air. Ground heating gives perceptible economical effect, which isexpressed by increase in vegetable crop capacity and especially by earlier dates of itsdistribution.

For soil heating mainly steel, and rarely cement pipes are used. Lately, in the soilheating systems polymeric pipes, and also armored panels (flooring) with round andoval cross section get more and more widespread.

As a heat carrier, for soil heating systems using the ferro-concrete hollow-core panels,highly mineralized geothermal waters are used. At the temperature 40-50 directflow heat supply scheme is recommended, and at the temperature exceeding 50 two-loop system. The methods of thermal calculations of the ground heating systems[10] permit to define the optimal amount of heat in order to reach the requiredtemperatures in different parts of a greenhouse.

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Complex systems of using geothermal waters for heat supply of hothouses are

recommended. As could be seen from fig. 3.13 geothermal water is given in seriesfirst to the heaters, then to contact heat exchanger for heating the supplied air andfinally for heating the soil. The indicated system is highly effective, as it permits touse fully the thermal potential of geothermal water.

The seasonal character of goods production necessitates the development of therefrigeratory chain for storage of food stocks. Among the existing methods of

processing and keeping perishable food, freezing of fruits and vegetables is the mostprogressive method of preservation. In frozen fruits and vegetables, the taste, aroma,appearance, main vitamin content and nutrients are preserved in the best way. Thismethod of storing perishable food permits to save 30% of energy inputs compared to

thermal canning of products [29].

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Execution of plans to be performed with minimal expenditures is possible by usingammonia-water absorptive refrigeratory plants with the use of heat of geothermalwaters. On fig. 3.14 [6] is presented the basic diagram of ammonia-water absorptiverefrigeratory machine functioning on the basis of heat of geothermal waters.

Absorptive ammonia-water machine serves for production of cold with thetemperature of 18 , which is required for cooling the refrigerator chambers andalso for getting block ice in the ice generator of brine cooling. As seen from fig. 3.14,geothermal water with 90 temperature is supplied to the generator of absorptiverefrigeratory machine. Ammonia vapors, formed as a result of boiling the ammonia-water mixture in the generator1, after passing the rectifier (2) condense in thecondenser (3). From the condenser liquid ammonia goes to the evaporator (5) throughan expansion valve (4). Ammonia vapors, formed in the evaporator as a result ofapplying the heat from the object to be cooled, are supplied to an absorber (6), whereit is absorbed by weak liquid and resultantly received strong liquid is directed to thegenerator (1) again by pump; the cycle is repeated. The work of the absorptive

refrigeratory machine in the specified regime does not raise any doubts and doesntrequire experimental researches to be carried out.

For supporting the optimal temperature-moisture regimes (t = 2...4 , = 85-95 %)in the refrigerated fruit and vegetable storage rooms there is a new possibility forMoldova to offer the system of cooling the air in the fruit and vegetable storehouseswith the help of sorbent solutions which use the discharged thermal water (fig. 3.15).The principle of processing the air is based on using the ability of chemical solutionsof different salts (sorbent) to absorb the moisture. The processes of preliminary dryingof air by liquid sorbents enable to bring the conditioned air subsequently to therequired parameters by inexpensive methods of direct evaporative cooling (adiabaticmoistening). This increases the chances of realization of the technological airconditioning in fruit and vegetable storehouses and the

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Fig.3.14 Basic diagram of ammonia-water refrigerating machine working on the basisof geothermal water

1- generator; 2-rectifier; 3-condenser; 4-expansion valve; 5-evaporator; 6- absorber;7-refrigeration chamber

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units of agroindustrial complex, where along with reduced temperature (4 ) highrelative humidity of the supply air is required (9798%).

Conclusions made by many authors [17,27,28] indicate the high efficiency of using

the air conditioning plants with liquid sorbents. At similar energy inputs they permitto get three times as much cold as in Freon or gas compression refrigerating systemsand 30% more than in absorptive refrigerating machines.

On fig. 3.15 [28] a basic diagram of air processing by sorbent solutions fortechnological air conditioning is presented.

Passing through the device 1, the processed air contacts with sorbent solutions. First,the air is dried up and slightly cooled, then, passing through the spray (or climbing-film or checker) chamber 2, contacts with continuously circulating water; it is cooleddown and becomes moist adjusting to the technologically required parameters; afterthat it is supplied to building by the fan 3. After passing through chamber 1, the part

of the depleted solution is pumped over into the solution-regenerating chamber 4. Theregenerated solution is heated up in the countercurrent heat exchanger 5 by discharged

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thermal water; this leads to evaporation of the earlier absorbed moisture andrestoration of initial sorbent concentration. The restored solution makes for the dryingroom 1 again and the cycle is repeated.

As it was already mentioned above, the air-cooling system with liquid sorbent can besuccessfully used for realization of technological air conditioning. For example, fordrying and cooling grain on an elevator it was developed a scheme by usinggeothermal waters. For cooling the atmospheric air specially developed air-coolers areused. There, film tower-coolers and central conditioners are used as heat exchangers.When air consumption is 30-thousand m3/hr, its temperature goes down to therequired 5-10 . This air is supplied to the grain coolers. The grain cooler consists ofan upper bin with dissectors for distribution of grain flow through four grate channels,three refrigerating convective zones, lower bin of two discharge facilities and theventilator of cooled air supply.

Grain with the temperature of 35 goes from grain-dryers to the upper bin. In thefirst refrigerating zone air is supplied with the temperature of 15 , in the second and

third zones it is supplied with the temperatures of 10 and 5 correspondingly. Thewidth of blown-off layer of grain in the first zone equals 200 mm (single-pass airmotion). The duration of grain being in a cooler is 30 min; total air consumption is 60thousand m3/hr. On passing through the cooler 50 tons of grain per hour, it coolsdown from 35 to 18-20 , on passing 25 tons per hour, its temperature goes down to8-10 . Grain from the receiving apparatus is supplied to the upper bins throughtransport communications. From the upper bin moist grain, by gravity, goes to twosimultaneously working grain-dryers, which are supplied with the air at thetemperature of 50-60 heated in water-and-air heater. Then grain goes to the nexttwo grain-dryers for final drying; from there it goes to the cooler. The cooled graingoes to the storage silo where it is prepared and sent for keeping. [11].

Refrigerated processing and storage of perishable phytogenic products is providedwith the cold less than 10% of the needed. Transition to modern refrigeratingtechnology of processing and keeping vegetables, melons and pumpkins, fruits and

berries is possible only by creation of rural refrigerating complexes, located close tothe regions of their growing. However, increasing the crop growing without havingthe resources for its keeping is unprofitable, as it increases the losses that are higheven without it.

Acceleration of development of the refrigeratory economy in the fields ofagroindustrial complex is possible only by introduction of cold supply systems basedon the using of local nontraditional energy resources with minimal expenses. Thesystems using absorptive ammonia-water refrigeratory systems and technologicalsystems of air conditioning with liquid sorbents on the basis of geothermal sources arethe most viable. The example can be the technological systems of air conditioningwith liquid sorbents on the basis of discharged thermal waters (fig. 2.16) developedfor tobacco factories [27]. Outdoor air, which is dried by liquid sorbents before, is

brought to required parameters by direct evaporation cooling. Discharged geothermalwater serves for heating the weak sorbent solution in the heat exchanger 1 anddischarged air from tobacco-drying ovens serves for desorption of the solution. As aresult of contacting with air in desorber 2, concentration of the solution increases.

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Strong solution, cooled by tap water in the heat exchanger 3, is directed to the filmdevice 4, where it dries outdoor air. Then, passing through the spray chamber 5, theair contacts with the circulating water, cools down and becomes moist until it adjuststo required parameters, after that it is supplied to factory sections by a ventilator forcarrying out technological systems of air conditioning and pre-technological keeping

of raw materials. It is not difficult in exploitation and does not require highly-skilledpersonnel. The similar systems can be successfully used for creation of optimalmicroclimate conditions in fruit and vegetable storehouses at keeping tuberous rootand juicy vegetative primary goods. Fruit and vegetable storage rooms are highlyrequired to support given moisture regime compared to keeping meat, cheese andother refrigerated products [40]. This can be explained by physiological features ofthe product, whose cells keep on living in the keeping process and it leads to the lossof dry substances and moisture. Therefore, in the fruit and vegetable storage rooms itis necessary to create viable conditions for them and simultaneously slow down

biochemical and breathing processes. Relative humidity of air in the chamber affectsthe process of evaporation of fruit and vegetable moisture and makes changes in their

breathing, which is reflected on normal flow of metabolism. For reducing the loss offruit and vegetable moisture it is desirable to support the relative humidity near thevalue of 100%. In such a way, the system of processing supply air with liquidsorbents is the most effective for supporting optimal moisture regimes at keeping

juicy vegetative raw materials. The basic diagram of cooling the supply air in fruitand vegetable storehouses by its processing with sorbent solutions, when usinggeothermal waters, is presented on fig. 3.15.

If the temperature of geothermal sources is high enough, then the offered system of

cold supply of fruit and vegetable storehouses can be successfully applied to all farmslocated in the coverage area of geothermal bores. This will give the possibility to save

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more than 1 million kWh of electric energy on each fruit and vegetable storehousewith the capacity of 1000 tons annually.

Using thermal waters for energy supply of tobacco factories, which require biggeramounts of heat and cold for technological purposes, can also be considered quiteinteresting. The existing system of energy supply of tobacco factories, which useheavy oil burners, are lower in efficiency. This leads to reduction of tobacco quality,deterioration of working conditions, decrease in factory productivity, unreasonablyhigh fuel consumption and pollution of the environment.

For improvement of heat supply systems of technological processes of tobaccoprocessing and improving the consumption of energy resources, it is necessary tochange the existing systems of energy supply with new and more efficient systems.Solution to the tasks mentioned above can be found by using geothermal waters.

A standard tobacco factory was chosen for studying this question and realizing itpractically. A basic diagram developed for given specific conditions of heat and cold

supply of the tobacco factory can also be applied to other tea factories located neargeothermal sources. Therefore, it was developed a complex scheme of energy supplyof a tobacco factory on the basis of geothermal sources to solve the problem of costsand profitability of using heat of thermal waters for energy supply of tea factories.[16]

Practically, hot air received by heating with geothermal waters can provide theprocesses of withering and predrying of tea to be carried out. For drying of tea it isnecessary to raise the temperature potential of thermal water to 105-110 or providedouble-stage air heating: first stage by thermal water, second by water vapor orelectricity.

As it was already mentioned, technological air conditioning can be realized by usinginexpensive conditioning systems, which use sorbents and the heat of dischargedwater.

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In that way, problems of thermal processing of tealeaves (withering, predrying,drying), pre-technological storage of raw materials and technological conditioning ofthe air in factory shops are solved complexly by using thermal waters.

The basic diagram of complex heat-cold supply of standard tea factory on the basis ofgeothermal sources is presented in fig. 3.18.

Thermal water from the bore 1 with the temperature of 95 arrives in the water-and-air heater 2 of the tea drying oven 5 and heats the air to the temperature of 75 ,subsequent heating of air to the required temperature 100 is carried out on thesecond stage in the steam-and-air heater 3. The air heated to 100 is blown into thetea drying oven 5 by the ventilator 4 and is used for drying the tea [25].

Thermal water discharged from the heaters 2 with the temperature of 87-90 goesinto the water-and-air heaters 6, where it heats the air to the required temperature,

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then this air is blown into the tea fixation-withering aggregate 8 by the ventilator 7and is used for withering (predrying) of tealeaves.

The discharged thermal water with the temperature of 70 75 accumulates in the

collector K and then can be used by residential consumers as well as for technologicalair conditioning in factory shops according to the scheme mentioned above (see fig.3.16).

In the regions with limited thermal water resources the scheme of direct hotwater supply only should be used; heating loads should be covered from othersources. Temperature of thermal water should not be below 40

In the regions with considerable resources of geothermal waters it isrecommended to use the scheme of direct-parallel supply of geothermal waterfor heating and hot water supply. At the water temperature of 70-80 andlimited geothermal resources it is recommended to use the scheme ofgeothermal water supply for heating by ventilation and hot water supply inseries.

With the rise of role of hot water supply in the total thermal load, it isrecommended to use non-dischargeable system of geothermal heat supply to

provide minimal consumption of geothermal waters.

In the regions with limited resources of geothermal waters, with high cost oftheir production and transportation, the heat pump system or other heating

plants should be used

To summarize, complex usage of geothermal waters in the systems of heat-coldsupply of technological consumers of agroindustrial complex will significantly savefuel-energy resources and permit to optimize the structure of fuel-energy balance of aregion, it will also create definite prerequisites for protection of the environment.

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3. Ahmedov Ia. B. Perspectives of renewable energy sources use . . . . " " 1999 #3. . 3-20.

4. Betaneli K.P., Kakabadze V. Sh. et al Main trends of complex and rational useof energy sources in Georgia until 2010

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2010 . "., 2000, 306 .

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. -- ., , 1998, 232 .19. Kays V.M, London A.L. Compact heat exchangers

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