Cogeneration—the development and implementation of a cogeneration system for a chemical plant, using a reciprocating heavy fuel oil engine with a supplementary fired boiler

Abstract

The contribution of cogeneration plants to a reduction in primary energy consumption will be important not only in lowering emissions to the atmosphere but also in cutting production costs by increasing the overall efficiency of fuel conversion to the electricity and heat used by process industries. This paper demonstrates the importance of the interactions of the utility needs of a process with the development and design of a cogeneration system to maximize fuel efficiency and achieve environmental compliance for a chemical plant. The cogeneration system in this project is based on a diesel cycle engine burning heavy fuel oil (HFO), driving an alternator and with an exhaust gas heat recovery boiler supplementary fired with either HFO or natural gas. The normal operation of the cogeneration plant is with the engine running at 95–100 per cent maximum continuous rating (MCR) with the supplementary firing of the boiler modulating to meet the process requirements for saturated steam at 10 barg. In addition to recovering waste heat from the engine exhaust gas (EEG), supplementary firing using the excess oxygen in the exhaust gas enables the process steam required by the plant to be produced without the loss of energy involved in heating combustion air. At the same time the reduced volume of oxygen available to the flame reduces peak temperature and NOx emissions, this being further enhanced by the phased combustion design of the burner. The technology demonstrated in this application is generally as used in gas turbine cogeneration cycles burning natural gas. The use of HFO in this instance necessitated the use of a reciprocating engine driven generator and the development of supplementary firing of the exhaust gases. The successful development of the technology enables this reciprocating engine based cogeneration system to be scaled up or, possibly more importantly, down utilizing HFO, natural gas or renewable derived liquid or gaseous fuels. Its implementation using spark ignition engine generators retrofitted to economic boilers may be one way general industry in the United Kingdom might meet its climate change levy (CCL) targets for energy reduction and help approach the government's carbon reduction requirements.