The economics of flue gas cooling technology for coal-fired power stations with flue gas desulfurisation

Pierru Roberts,Gerrit Kornelius,Oleg Bosyi,Cj Luther Elsa

doi:10.17159/2410-972x/2018/v28n1a8

Abstract

Developments in heat exchanger technology, specifically in the use of polymers as tube material, have allowed the use of gas to water heat exchangers under conditions previously not viable. Two applications in the flue gas cleaning circuit of coal-fired power stations are described in this paper. In conventional pulverised coal-fired boilers, cooling of gas prior to the wet flue gas desulfurisation (WFGD) absorber reduces water consumption for evaporative cooling of the flue gas and can recover heat for feed water preheating or for use elsewhere in the plant. In another application, circulating fluidised bed boilers, which are currently proposed for a few independent power producers and may not require wet FGD, heat recovery is still feasible upstream of the bag filter typically used for particulate emission control. The extracted heat can again be recovered for use in other power plant processes, in this case most economically for pre-heating combustion air. This paper presents case studies for each of the above applications, showing that the power station efficiency is typically increased by approximately 1% of its pre-installation value. An economic analysis is provided for each, including additional power sales, reduced water consumption, or reduced fuel use with a reduction in carbon tax. For the larger installations with WFGD, payback time can be in the order of 6 years.

Highlights

In arid countries such as South Africa the reduction of water use in industry is especially important
If the inlet gas is cooled before entry into the wet flue gas desulfurisation (WFGD) by an external heat exchanger, and the heat is used elsewhere in the power circuit, there is an obvious benefit in water savings
Even in power generation applications where WFGD is not practised, such as in circulating fluidised bed (CFB) boilers, the recovery of heat from the flue gas and the use thereof in other parts of the circuit may lead to similar benefits for these applications

Summary

Introduction

In arid countries such as South Africa the reduction of water use in industry is especially important. Even in power generation applications where WFGD is not practised, such as in circulating fluidised bed (CFB) boilers (with the addition of limestone directly to the boiler), the recovery of heat from the flue gas and the use thereof in other parts of the circuit may lead to similar benefits for these (usually smaller) applications. Heat transfer takes places via an intermediate closed loop (as for the WFGD) to the combustion air (both primary and secondary) of the fluidised bed, or to the feedwater Such a flue gas heat recovery system will for example be installed at the 299MWe Teesside power station in the United Kingdom, which is the world’s largest CFB utilising only biomass as fuel. The annual maintenance time was taken as 42 days and availability during run-time as 99.6%

Design electrical output

Findings

Conclusions