PR. Termodinamika 2 B # 4

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1 PR. Termodinamika 2 B # 1. Problem Problem PT. PLN mengoperasikan beberapa pembangkit listrik tenaga uap (PLTU) dengan bahan bakar batubara. Lakukanlah studi dari media (elektronik atau etak) tentang kapasitas terpasang PLTU PLN dan konsumsi batubara tahunan semua PLTU tersbut. Berdasarkan dasar-dasar termodinamika yang sudah saudara kuasai, lakukanlah analisis kasar tingkat efesiensi termal sistem pembangkitkan listrik PLN. Berikanlah rekomendasi/komentar saudara. Saudara bebas mengambil asumsi, namun tuliskanlah dengan jelas.. Problem Problem 9.10

2 Refrigeration & Gas Liquefation Refrigeration: Obtaining temperatures that are lower than the surrounding temperature 2 nd Law of Thermodynamis: " It is not possible to have a system that operate ontinuously in transferring heat from a lower temperature reservoir to a higher temperature reservoir without an aid of energy from outside of the system Thermodynamis 2009 Q Q igher Temperature eat Reservoir igher Temperature eat Reservoir Ws ηt = = Q ( T T ) T C Ws Expander Ws Lower Temperature eat Reservoir Lower Temperature eat Reservoir Q C Q C eat Conversion into Work Cyle Refrigeration Cyle 1

3 Coeffiient of Performane (COP): Q Q COP = = W Q + Q S T S = T S T S C T = T T T = T T We spend W s to remove Q from lower temperature heat reservoir COP is normally > 1.0 Illustration: A proess need refrigeration load 2 MW. This refrigeration is used to maintain a ool proess at -2 o C. Sine the plant is loated in northern oastal region of Central Java Provine, the surrounding temperature is around 29 o C. Estimate minimum power onsumption to operate the refrigeration system. Calulation: Q := 2 MW T := ( ) K T := ( ) K T COP := T T Q Ws := COP COP = 8.72 Ws = kW An important fat to note: we an move muh higher quantity of heat utilizing a given amount of power Consider now: From energy balane for flow proess: Ws ( Q + Q ) = 0 + C For an illustration onsider the previous example: Q := ( COP + 1) Ws Q = 2.229MW Do you have any idea to utilize this amazing phenomena? Or: Q = Ws + QC = ( COP + 1)Ws We an get even muh higher Q for a given amount of Ws 2

Gas Liquefation Gas Critial point Liquid Liquid-vapor mixture Vapor Solid ow an we bring system from gas region into vaporliquid mixture region?

4 Gas Liquefation Gas Critial point Liquid Liquid-vapor mixture Vapor Solid ow an we bring system from gas region into vaporliquid mixture region? LNG Plant Refrigeration The most ommon refrigeration methods in industry: 1. Mehanial vapor ompression yle: mehanial energy 2. Absorption Refrigeration : Thermal Energy. Jet Steam Cyle : internal energy

5 Similarities & Differenes Among Refrigeration Systems Vapor Compression Refrigeration Steam-Jet Refrigeration (or Expansion Engine) Absorption Refrigeration Vapor Compression Cyles Standard Vapor Compression Cyle Condenser Exit Evaporator Exit

Atual Vapor Compression Cyle Sample Case: A refrigeration system operating on vapor ompression yle using tetra fluoroethane refrigerant, CF C 2 F (FC 1-a).

6 Atual Vapor Compression Cyle Sample Case: A refrigeration system operating on vapor ompression yle using tetra fluoroethane refrigerant, CF C 2 F (FC 1-a). Refrigerant temperature at ooling oil is -10 o F. System apaity is 10 ton of refrigeration (1 ton of refrigeration is equal to BTU/hr). a. If the refrigerant exit the ondenser and evaporator as saturated liquid and vapor respetively, determine COP, rate of refrigerant irulation and power required to run the system. b. Rework part a if operating pressures are equal to part a, on the other hand the refrigerant exit the ondenser 10 degrees Fahrenheit below its saturated temperature. Saturated -10 o F Saturated 5

7 Some modifiations: Multi stage refrigeration system Using expansion engine (isentropi) instead of expansion valve (free throttling) Two Stage Refrigeration System Steam Ejetor Refrigerator -200 o C 6

8 Sample Case: To fulfill the need of hilled water (10 o C) a hemial plant will build a steam ejetor refrigerator system. In the refrigeration yle hot ooling water at 5 o C is mixed with make-up water at the same temperature and then expanded through a spray nozzle into the spray hamber that is maintained under vauum. Part of the water will evaporate and hene ool the water to temperature of 10 o C. If the ooling load of the plant is 10 6 BTU/hr, determine the ooling water irulation rate and the rate of make up water. ( W + M ) = V. V + W. hl W V = M = V ( hl ) ( ) V Absorption Refrigeration Air Compression Refrigeration System Expansion Engine Why expansion engine should be used instead of expansion valve? 7

9 Disuss a ase for Air Compression Refrigeration System Regenerator 5 Strong Solution 8 Kondensor 9 Weak Solution Refrigerator Absorber See the word doument T Gas Liquefation Critial point Liquid Phase Two-Phase Region S B A A 1 2 Gase Phase Priniple: bring the gas into two-phase region 1. Cooling gas at onstant pressure (path 1): requires a large heat transfer area sine heat transfer oeffiient for gas phase is very small 2. Isentropi expansion (path 2): need equipment ost for turbine or expansion engine (rather expensive). Isenthalpi expansion with expansion valve (path ): low ost of equipment for equipment but need high initial pressure.. Modifiation of path : isentropi ompression isobari ooling isenthalpi expansion 8

Liquefation via Free Throttling (Joule-thomson Liquefation) Liquefation via Expansion Engine (Claude Gas Liquefation) 29 K 00 K Basis: 1 unit mass of stream 1.

10 Liquefation via Free Throttling (Joule-thomson Liquefation) Liquefation via Expansion Engine (Claude Gas Liquefation) 29 K 00 K Basis: 1 unit mass of stream 1. = x 6 + (1-x) 8 x = bar Saturated liquid Sample Case: Natural gas whih an be onsidered pure methane is fed into a ooler of Linde proess at 180 bar and 00 K. The lower pressure methane leaves the ooler at temperature 6 o C lower than the temperature of the high pressure inoming methane. The separator is operated at 1 bar and the produt is saturated liquid. What is the fration of the methane entering the ooler that is liquefied. 9

11 eat Pump eating Capaity: ( COP +1) Ws Q =. Cooling Capaity: Q = COP. W s 10

Analysis of a Refrigerant Compressor Load Stand Incorporating Hot Gas Bypass and a Single Full Condensation Heat Exchanger

Purdue University Purdue e-pubs International Compressor Engineering Conferene Shool of Mehanial Engineering 1984 Analysis of a Refrigerant Compressor Load Stand Inorporating Hot Gas Bypass and a Single