www . refrigerationandaircon . co . za RACA Journal I June 2023 49
Technical
Table 1 : The Carbon Dioxide Emission Coefficients in USA are as follows 4 :
Pounds CO 2 Per Million Btu
Natural Gas 116.65 52.91
Coal - Anthracite 228.60 103.69 - Bituminous 205.57 93.24 - Subbituminous 214.13 97.13 - Lignite 216.40 98.16 - Coke 250.59 113.67
Diesel and Home Heating Fuel ( Distillate Fuel Oil )
163.45 74.14
Kilograms CO 2 Per Million Btu
Table 2 : Typical thermal efficiencies for power generation options 5 : Type of Fossil Fuel / Atomic Energy Facility Natural Gas — Peak Power Turbine 25 %
Thermal Efficiency
Nuclear Power 6 , 7 30 % -33 % Coal-Steam Cycle 38 % -45 % Nuclear — Pebble Bed Modular Reactor 8 45 % Coal — Gasification Combined Cycle 48 % Natural Gas — Combined Cycle 50 % -56 %
Future ( 2010 )— Natural Gas and Coal Combined Cycles
60 % Future ( 2015 )— Fuel Cell Combined Cycles 70 %
Table 2 lists thermal efficiencies for power generation . Using natural gas for peaking power is about half as efficient as the combined cycle option . Trigeneration systems can have overall efficiencies of around 80 %. As per Energy Efficiency Services Limited ( EESL ), tri-generation can reduce the end user ’ s primary energy demand by 60-70 %, increase overall energy efficiency by almost 75 %, and cut greenhouse gas emissions by up to 30 %. The trigeneration system can provide 300 tonnes of refrigeration for every MW of power it generates , saving up to 195kW of electricity , and eliminating the need for investments in centralised cooling equipment and hot water boilers . Further , by creating a parallel source of electricity through captive generation , trigeneration can protect consumers against surging tariffs . 9
The integration of the tri-generation plant with the site infrastructure to has to be carefully considered when sizing the system to ensure that the most efficient solution is achieved . By correctly sizing the plant , it will not only increase the efficiency of the building , but it will also be the most cost effective to maintain and provide years of reliable service .
System utilisation is of utmost importance ; therefore , any excess hot water ( water not used by the absorption chillers ) will be used for space heating ( or other heating needs ). Hot water will be supplied to Fan Coil Units by means of piping and plate heat exchangers .
We believe that tri-generation and quad-generation technology is here to stay , and we will see more and more similar plants erected in the near future . RACA
When electrical power is generated , the energy in the fuel ends up as electrical power or as waste heat . When the fuel is used to power a heat engine , there are boundaries that determine the maximum quantity of the fuel energy that can be converted to electricity . A large amount of waste heat is given off at the power generating plant by the power cycle that drives the generator . The thermal efficiency of the power generation is defined as the electrical energy produced divided by the total energy released by the fuel consumed . The excess heat of the power cycle is rejected to cooling water systems as well as the exhaust gases that exit from the power plant stacks . Typically cooling towers or dry coolers reject the heat to the atmosphere , but there are other means to reject the heat like distributing the hot water to residential , commercial or industrial use .
“ Quad-generation plants are uniquely positioned in the industry in that they can provide reliable clean power around the clock – unlike solar or wind power plants which depend on the natural environment to generate power .”
4 https :// www . eia . gov / environment / emissions / co2 _ vol _ mass . php 5 Sustainable Nuclear Power , 1st Edition - December 8 , 2006 , Galen Suppes , Truman Storvick , eBook ISBN : 9780080466453
6 http :// www . uic . com . au / nip57 . htm reports 33 % thermal efficiency for nuclear power as reasonable assumption and high energy output as compared to energy input .
7 http :// www . nucleartourist . com / world / koeberg . htm confirms 33 % efficiency after improvements
8 http :// www . worldandi . com / public / 2001 / April / nuclear . html . 9 https :// www . iiec . org / sdc / SDC _ Tri-generation _ factsheet . pdf
www . refrigerationandaircon . co . za RACA Journal I June 2023 49