Trigeneration technology as a green technology is receiving more interest locally, resulting in its increased implementation.
Trigeneration technology has the same components as a cogeneration plant – a gas engine, electricity generator and a heat exchanger – but also includes an absorption chiller that uses waste heat from the gas engine to produce cooling.
The growing interest and investment in the technology is because more businesses, commercial park or precinct owners are recognising that trigeneration is more commercially viable compared to coal-fired and natural-gas-fired power generation, or other sources of renewable-energy generation, says engineering and design company WSP director Pieter de Bod.
Trigeneration uses the fired power generators, including gas-turbine technology, using the waste heat from the operation of the trigeneration system to generate cooling or heating, which reduces a building’s reliance on the electricity grid.
While electric-driven compression chillers can provide cooling, the recovered heat by the trigeneration power plant can be used to drive the absorption or adsorption chillers to reduce the overall cooling demand of the building.
“These trigeneration power plants with absorption chillers continue to gain market acceptance, owing to their ability to produce cooling using heat, not electricity.
“When compared with cogeneration, trigeneration can be up to 40% more efficient, further reducing operating costs, fuel expenses and environmental pollutants. The trigeneration systems, therefore, benefit not only the building owner but also society in several ways, including increased power reliability, reduced carbon emissions and power requirements on the electric grid, and reduced dependence on coal or fuel oil,” De Bod explains.
Meanwhile, other advantages of using high-methane gas as an energy source and substitute for coal are the cleaner burning process of the fuel and heat energy recovery, providing an overall higher efficiency, he adds.
Although trigeneration is still a new practise in South Africa, De Bod highlights this technology is used worldwide in the US, Europe, China and Japan, for instance, owing to the carbon emissions reductions that can be achieved from using this technology in power generation.
“A study undertaken in 2011 by manufacturer of adsorption chillers and factory-built high-efficiency trigeneration systems Power Partners design engineer Wes Livingston, in the US, demonstrated that a facility or building that properly uses a trigeneration system burning natural gas may emit up to 25% less carbon emissions a year than a traditional building using supplemental solar photovoltaic power,” De Bod says.
Although renewable technologies, such as solar cells, do not emit any carbon emissions while operating, he notes that the emissions do occur from the grid when solar power is not available, for instance, owing to heavy clouds, night-time and shading.
In addition, any heating or cooling needs at the facility or building are generally produced by equipment, such as electromechanical chillers, which consume significant amounts of electricity, he points out.
“However, an on-site trigeneration system burning natural gas simultaneously produces electricity, heating and cooling - up to 30% to 40% more efficiently.”
Nevertheless, De Bod notes that the biggest consideration in terms of viability for this system in South Africa would be the availability of gas resources, including sufficient piped-gas capacity at realistic tariffs and escalation.
“Currently available gas is natural fossil gas – with a high methane content of about 91% – that is piped from the Mozambique gasfields to South Africa. Petrochemicals company Sasol currently distributes this gas, but in terms of the latest determination by the National Energy Regulator of South Africa, it appears that the gas will also be controlled by authorities from this year.”
De Bod adds, however, that there is significant room for increased capacity of gas infrastructure, as this resource is “currently not available everywhere”.
A second consideration is the integration of the trigeneration plant with the site infrastructure, as this has to be carefully considered when sizing the system to ensure that the most efficient solution is achieved, he says.
“Correct sizing of the plant will not only increase the efficiency of the building but it will also be the most cost effective to maintain, providing years of reliable service.”
There are currently only two operational trigeneration plants in South Africa, one at telecommunications company MTN’s head office, in Fairlands, and financial services firm Standard Bank’s new premises, in Rosebank, both in Gauteng. Both mechanical components were designed by De Bod, who was formerly employed by RPP Consulting Engineers, which joined forces with WSP in April this year.
However, there are several other plants under development, as government and industry are increasingly considering distributed power generation as one of the best medium-term mitigation measures to combat power capacity shortages, De Bod says.
“In light of this, WSP believes that more similar plants will be erected in the near future,” De Bod concludes.