Improving the performance of geothermal power plant by substituting water steam power plant for the binary power plant

Transcription

1 oak, orsukieicz-ozur an Stachel Imroving the erformance of thermal oer lant by substituting ater steam oer lant for the binary oer lant Wlaysla oak, Aleksanra orsukieicz-ozur an Aleksaner A. Stachel Technical University of Szczecin, al. iasto 7, L Szczecin, olan anrzej.stachel@s.l Keyors: thermal energy, thermal oer lant, binary oer lant ASTRACT The aer resents a mathematical moel of a oer lant to variants: a ater steam oer lant using fossil fuel an thermal energy an a binary oer lant ith ater an organic substance as orking meia, oere ith fossil fuel an co-oere ith thermal energy. oer an efficiency calculations for a binary oer lant have been erforme, an the results have been comare ith oer an efficiency values obtaine for a conventional oer lant ith ater as orking meium. The calculations have been mae ith an assumtion of a constant value of heat flux from fossil fuel an maintaining comarable orking conitions of the oer lan in all the variants consiere.. ITROUCTIO The starting oint for assessment of the effectiveness of oeration of ifferent oer lant esign is a single comonent suerheate cycle oer lant, here ater serves as circulation flui. Such oer lant ill be relace ith a binary oer lant oerating in the same range of high an lo reservoir temeratures. Heat transfer in the binary oer lant from the high temerature reservoir to the lo temerature reservoir takes lace in the heat exchanger of conenser/evaorator tye. In the aer resente an iscusse ill be schematics of oeration of both oer lants oerating in accorance to the Clausius-Rankine cycle. resente also ill be algorithms of calculation encomassing such quantities as efficiency an oers of resective cycles. Calculations ill be carrie out for selecte organic fluis of the loressure cycle of a to stage cycle. The results of calculations ill be resente in the form of relevant istributions enabling carrying out of a comarative assessment of a binary cycle an a single flui cycle, hich ill enable formulation of arising final conclusions. If you use equations, efine all symbols, either after the equation, or in a omenclature section at the en of the aer. 2. CALCULATIO METHOOLOY FOR ARTICULAR OWER LAT TYES resente belo are the relations use for calculations of articular steam oer lant variants, as ell as the assumtions an calculation roceure. 2.. Steam oer lant variant using fossil fuel an thermal energy In the first stage of the analysis, calculations have been carrie out for a steam-ater oer lant resente in Figure, oere from to sources: - suerheating, evaoration an heating of orking meium in higher temerature range the source of heat is fossil fuel, an - heating of orking meium in loer temerature range ith energy from thermal ater stream. The oer lant orks accoring to thermoynamically rocess Rankine cycle, hat is resente at Figure 2. Fig.. Scheme of a steam ater oer lant oere ith fossil fuel an thermal energy Fig. 2. Cycle of thermoynamical rocesses of steam ater oer lant In the calculations for variant rimary of the oer lant the folloing relations have been use. Heat flux sulie to the cycle from the boiler an thermal heat exchanger an use for heating, evaoration an suerheating of the orking meium has been calculate accoring to the folloing relation: Q & = + () k here: - heat flux transferre to the orking meium (ater) in thermal heat exchanger: ( h h ) & & (2) Q = m - heat flux sulie to the orking meium from the boiler (ater, steam):

2 oak, orsukieicz-ozur an Stachel ( h h ) = m& (3) k Heat flux carrie aay from the cycle in the steam conenser: () Q m 2 s 3 In the calculations of the oer of Clausius-Rankine cycle can be escribe relation for isentroic exansion rocess in the turbine: = C R m 2 s & () selecte organic meia belong to the grou of ry meia, for hich the suerheating rocess is not necessary, often even not avisable. This allos to avoi aitional energy inut for suerheating of orking meium. The uer cycle is oere entirely ith energy from burning the fuel in the boiler, hereas the loer cycle is artially oere ith the energy from the boiler an co-oere ith energy from thermal ater. or relation for energy balance equation: Q & = + = + (6) k from here after transformation: C R C R = (7) Efficiency of the Clausiusa-Rankinea cycle calculate from the folloing relation: η (8) C R C R = = Fig. 3. Scheme of a binary oer lant co-oere ith fossil fuel an thermal energy Heat flux use for heating of orking meium in the enthaly range from h to h, calculate from the formula: * + m& = m& c ( h h ) ( T T ) = 2 (9) here h eens on T. The calculations for rimary cycle ere base on the assumtion that the suerheating temerature of steam as 370 C at 3 bar ressure, corresoning to a ressure of 0.0 bar an steam humiity of x = 0,86 at the en of isentroic exansion in the turbine. The orking meium flo as assume at m& = kg s. The calculations have been mae for the assume value of thermal ater temerature T = 0-00 C. The thermal heat flux an thermal ater flo require to suly the re-heater of the oer lant can be calculate from formula (9) inary oer lant variant Another, secon variant of the oer lant, marke as binary lant, is resente in Figure 3. This oer lant consists of an uer cycle, here ater is use as orking meium, an a loer cycle, here the orking meium is one of a fe organic substances (, butane, isobutene,,, R2ca, R2fa, RC38). The oer lant orks accoring to thermoynamically rocesses Rankine cycle, hat is resente at Figure. It has to be emhasize that ater is a so-calle et meium, hich, eening on the assumtions regaring the oer lant cycle, shoul be suerheate to a smaller or larger egree before being sent to the turbine, hereas the 2 Fig.. Cycles of thermoynamical rocesses of a rimary oer lant Calculation methoology for uer cycle of binary lant The mathematical moel calculations of the binary oer lant is escribe by the folloing relations. Heat flux sulie to the uer cycle from the boiler use for heating, evaoration an suerheating of the orking meium calculate from the folloing relation: (0) Q m Heat flux carrie aay from the cycle for conenserevaorator tye of heat exchanger: & () Q Q s = m 2 s 3 For calculations of the oer of C-R uer cycle can be use relation for isentroic exansion rocess in the turbine: = C R m 2 s & (2) or transforme relation of energy balance equation: C R = Q (3)

3 Efficiency of the Clausiusa-Rankinea uer cycle calculate from the folloing relation: η () C R C R = = The element linking the uer an loer cycle (accoring to Fig. 3 an Fig. ) is a heat exchanger (evaoratorconenser), hose energy balance can be exresse as follos: ( h h ) = m& n & & () Q s = m 2 s 3 Using the balance equation for this exchanger can etermine the orking meium flo in the uer cycle as a function of the flo of meium in the rimary cycle. h2 s h & 3 n = m& (6) h h m Calculation methoology for loer cycle of binary lant Exresse belo are the mathematical relations for the loer cycle, in hich organic substance is the orking meium. The total heat flux sulie to the loer cycle from evaorator-conenser heat exchanger an thermal heat exchanger for heating, evaoration an suerheating of the orking meium (organic meium) have been calculate from the folloing relation: = Qs = m& n & + ( h h ) + m& = n Heat flux carrie aay from the cycle in the conenser: Q mn 2s 3 (7) (8) Analogical, for calculations of the oer of C-R loer cycle can be use relation for exansion rocess in the turbine: C R = mn 2 s & (9) or transforme of energy balance equation: C R = Q (20) Efficiency of the Clausiusa-Rankinea loer cycle calculate from folloing relation: η (2) C R C R = = Calculation methoology for binary lant The total heat flux transferre to the binary lant (binary cycles) is a sum of heat flux transferre to uer cycle an transferre in thermal heat exchange in loer cycle: Q & = + (22) It can be ritten: 3 oak, orsukieicz-ozur an Stachel ( h h ) + mn ( h h ) & (23) Q m Heat flux carrie aay from the binary cycle is equal to the energy flux carrie aay from the rimary cycle: & (2) Q Q = mn 2s 3 The total oer of the binary lant as calculate from the energy balance as a sum of the oer of uer an loer cycle: C R C R + C R = (2) The binary lant efficiency as calculate from relation: CR CR CR + η C R = = (26) + The calculations for the uer cycle of a binary oer lant ere carrie out an base on the assumtion that the conensation of steam takes lace at the temerature T 2s = T 3 = 0-80 C. The exansion rocess in the turbine takes lace from the same value of suerheate steam temerature as in the rimary cycle, an to the same value of steam humiity at the turbine outlet. The loer cycle oerates in the folloing temerature range: uer heat source ith a temerature of T = T = T 2s -?T, being the conensing steam, an the conensation oint of organic meium T s = 29 C, hich is the ater conensation oint in the rimary cycle. The temerature ifference beteen the conensing steam an the evaorating organic meium as assume at?t = 3K. The assumtions for thermal ater temeratures ere ientical as for variant, i.e. T = 0-00 C. 3. Results of calculations The calculations ere carrie out for the to variants of the oer lant. The exemlary results of calculations are resente in Table. These results ere taken from the ork []. In the aer resente have been The results of calculations to analyze variants of thermal oer lants have been resente on Figures - 8. On Figure resente is influence of evaoration temerature of meium in loer cycle on oer of binary oer lant (for isobutan) la t =80 C ierotny órny t [ C] olny inarny Fig.. Influence of evaoration temerature of meium in loer cycle on oer of binary oer lant (for isobutan)

4 oak, orsukieicz-ozur an Stachel On Figure 6 resente is influence of tye of meium in loer cycle on oer of binary oer lant. On Figure 7 resente is influence of evaoration temerature of meium an tye of meium in loer cycle on efficiency of binary oer lant. On Figure 8 resente is influence of meium tye an evaoration temerature of meium on thermal heat flux la t =80 C ierotny utan R2ca R2fa RC t [ C] Fig. 6. Influence of evaoration temerature of meium an tye of meium in loer cycle on oer of binary oer lant 3 hc-r [%] la t =80 C ierotny utan R2ca R2fa RC t [ C] Fig. 7. Influence of evaoration temerature of meium an tye of meium in loer cycle on efficiency of binary oer lant. 20 Q o la t =80 C ierotny utan R2ca R2fa RC t o [ C] Fig. 8. Influence of meium tye an evaoration temerature of meium on thermal heat flux Figures resent the turbine oer of articular oer lant variants as a function of evaoration temerature (organic meium). The analysis of this chart shos that the aitional suly of the oer lant ith a thermal ater stream ith secifie temerature allos to obtain higher oer values of the oer lant, hoever only after the introuction of binary cycle ith lo-boiling meium in loer cycle has it resulte in significant imrovement of the effectiveness of the oer lant. This results rimarily. from the fact that organic meia have much loer values of evaoration enthaly comare to ater, hich affects the amount of circulating meium in the cycle at the assume constant value of sulie heat flux. The analysis shos that the use of the binary solution ith lo-boiling meium in the loer cycle makes it ossible to make better use of the lo-enthaly thermal energy comare to a classical oer lant ith ater as a orking meium. This is relate to the fact that the heating enthaly of an organic meium is close an sometimes higher than the evaoration enthaly of that meium (eening on the tye of meium an roximity to the critical oint). 3. Conclusions The aer has resente a oer lant moel ith ater organic flui as orking meia, oere by fossil fuel energy an co-oere ith thermal energy. oer an efficiency calculations have been erforme, an the results for binary oer lant have been comare ith oer an efficiency values obtaine for a conventional oer lant ith ater as orking meium. The calculations ere mae using the assumtions resente in section 3, an the rimary assumtion for all the variants consiere as the maintenance of ientical orking arameters, i.e. the same temerature of the uer an loer heat source an a constant value of energy flux from fossil fuel. ase on the calculations erforme the folloing conclusion can be ran: - the use of organic meium in a binary oer lant allos for an increase of lo-temerature thermal energy share in the total energy flux sulie to the lant an for obtaining measurable benefits in the form of higher oer of the oer lant. Acknolegement The aer as elaborate ithin the frameork of the roject R finance by the olish Ministry of Science an Higher Eucation REFERECES ar O, robert S, O Callaghan W.: Selecting a orking flui for a Rankine-cycle engine. Alie Energy 98; 2: -2. Hung T.C, Shai T.Y, Wang S.K.: A revie of Organic Rankine Cycles (ORCs) for the recovery of lo-grae aste heat. Energy 997; 22 (7): Chmielniak T.: Technologie energetyczne (Energetic technologies), Wyanicto olitechniki Slaskiej, liice 200. Lauyn., alik M., Strzelczyk F.: Elektronie (oer lants), WT, Warszaa, 997 Mikolajczyk Sz.: Ocena orónacza efektynosci racy elektroni binarnej z zastosoaniem oy i niskorzacego czynnika organicznego z elektronia jenoczynnikoa, z turbina zasilana rzegrzana ara ona. Thesis. romoter: rof. Wlaysla oak. Szczecin University of Technolgy, eartment of Heat Engineering, (in olish)

5 oak, orsukieicz-ozur an Stachel Table. Summary of selecte calculation results for variant rimary an binary oer lant here organic meium is isobutan t t t o Q Q o η C-R η C-R * η C-R * L.. [ C] [ C] [ C] [%] [%] [%] [%] Q Q o η C-R , 6,0 983,8 3,89 32,37 327,2 90, 968,0 30,09 3, , 66,9 983,8 3,89 32,9 3292,2 286,3 972, 29, 32, , 87,8 983,8 3,89 32,82 337, 389, 978,0 28,98 32, , 08,7 983,8 3,89 33,0 363, 99, 98, 28, 33, , 29,6 983,8 3,89 33,28 36, 68,2 99,8 27,93 33, , 0,6 983,8 3,89 33,2 3669,0 76,8 006,3 27,3 3, , 7, 983,8 3,89 33, ,8 886, 020, 26,93 3, , 92, 983,8 3,89 3,0 399,6 039,3 036,8 26, 36, , 23, 983,8 3,89 3,26 066,9 207,6 06,8 2,99 36, , 23, 983,8 3,89 3, 233,0 39,8 08,0 2, 38, , 2, 983,8 3,89 3,76 22, 60,2 09,9 2,0 39, , 276, 983,8 3,89 3,03 6, 8,2, 2,67 0,9