44
Technical
TRI-GENERATION , QUAD-GENERATION AND DECARBONISATION
By Pieter de Bod , Pr . Eng , LEED AP BD + C , CDCP , Green Star SA AP
A tri-generation system with carbon sequestration is defined as a ‘ quadgeneration system ’, which is the production of electricity , heat and cooling from a fossil fuel like natural gas with the addition of recovery of carbon dioxide from engine exhaust to minimise harmful carbon emissions to the atmosphere . Tri-generation and quad-generation plants are truly marvels of ingenuity , engineering and forward-thinking design .
• Learn about the functionality and implementation of a tri-generation or quad-generation system
• Understand how absorption chillers play a role in trigeneration and quad-generation systems
• Recognise the benefits of carbon capture technology
Building owners or industrial businesses are increasingly seeking ways to use energy more efficiently as a direct result of some or all of the following factors : 1 . Dramatically increasing electric or energy rates 2 . Decreased power reliability ( blackouts , brownouts , rolling blackouts , and other power interruptions ) from the current power providers
3 . Competitive and economic pressures to cut operational expenses
4 . Reducing carbon emissions of air pollutants and greenhouse gases
Various technologies exist for clients that are looking to use energy more effectively and to decarbonise or achieve a net zero energy building ( NZEB ). A tri-generation or quad-generation system is a great alternative solution to their existing or new facility . This article will provide more information about the different types of tri-generation plants and look at quad generation and absorption chillers .
TRI-GENERATION OR CCHP A tri-generation plant is a plant that comprises mainly of mechanical and electrical equipment to simultaneously generate electricity , hot water or steam and chilled water in a very efficient manner and from a single source of energy . The main energy input to a tri-generation plant is typically natural gas or biogas . The high efficiency of a tri-generation plant is a result of efficiently recovering engine heat produced by the power generator and using that heat to generate hot water or steam for buildings or industrial processes , or to generate chilled water or ice making for ice storage . This technology is also called a Combined Cooling , Heating and Power Plant or CCHP .
Methane rich natural gas , a fuel with a high methane content of between 70 % -90 %, allows for a cleaner burning process ( in comparison to diesel fuel ) and this allows harvesting of the heat with minimal clogging of the heat recovery devices . Harvesting heat from diesel fuelled power generators is hampered by the increased accumulation of soot on the exhaust heat recovery devices . Even with the best technology available , most diesel generator sets typically only convert about 33 % of the energy stored in the fuel into electricity . 1 In other words , for every three barrels of diesel combusted , about only one barrel is converted to electricity and the remaining two barrels are discarded as waste heat in different forms . The phenomenon occurs due to the incomplete combustion of the fuel in the engine and other losses as friction .
CO-GENERATION Co-generation , also known as combined heat and power ( CHP ), is the simultaneous production of only electricity and heat but lacks the cooling generation component . CHP systems are implemented where cooling is not required . Cogeneration systems can also be equipped with carbon capture technology . Cogeneration plants are less efficient than tri-generation or quadgeneration plants and require lower capital expenditure .
44
1 Rehman et al ., 2007
RACA Journal I June 2023 www . refrigerationandaircon . co . za