Abstract
Growing environmental restrictions in energy production industry calls for greater efficiency and cleaner fuel burning processes. Biomass (wood chips) as a fuel is in great demand for boiler and power plants as it is considered widely available and relatively clean. While combining woodfuel flue gas and condensing economizers significantly raises the efficiency and makes it even more viable solution for energy production although the biomass fuel usage still has reservations in waste heat, which could be utilized. The calculation algorithm is presented for evaluation of subcooled biomass flue gas components concentration values which determine the leftover heat energy value carried by flue gas flow. Several cases of biomass quality (regarding moisture w=45%, 50%, 55% and 60%) and combustion process quality (regarding air excess value λ=1,2; 1,5; 1,8) in the flue gas temperature range of 50 to 20°C and effects for flue gas internal dynamic were examined. It was determined that water vapour amount depends only on temperature, while every other component concentration change with different air excess and temperature values. It was observed that further usage of biomass flue gas could result in up to 13% additional heat energy recovery for 1MW of fuel input, system combination together with condensing economizers could result in up to 31% of heat energy recovery.
Highlights
Nowadays European energy sector is arguably well invested in biomass industry in compliance with recent regulations issued by the EU
When flue gas temperatures are below dew point ts and part of water vapour turns into condensate, the additional tws dependence subject to ts comes into effect
That means that the amount of water vapour in the supercooled flue gas mixture depends strictly on the flue gas temperature
Summary
Nowadays European energy sector is arguably well invested in biomass (wood fuel) industry in compliance with recent regulations (mainly directive 2010/75/EU) issued by the EU. It is still conceivably not reaching full potential. In this article the algorithm for evaluating flue gas components below flue gas mixture’s dew point is presented which is essential in finding how much of low-grade heat energy can be utilized in additional heat utilisation processes (i.e. with the application of heat pump). The low-grade heat value that could be recovered is calculated via 50% biofuel moisture w and previously mentioned air excess values λ when fuel energy input is 1MW
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