System for recovering heat from flue gas, control arrangement for use in such a system and a method performed by such a control arrangement

A heat recovery system using feed water from a feed water main system as a heat carrier for recovering heat from flue gas generated by combustion at a biomass plant installation, the heat recovery system comprising

• a heat recovery fluid circuit fluidly connected to a feed water main system via a heat recovery circuit inlet and a heat recovery circuit outlet in order to circulate feed water as a heat carrier in the heat recovery circuit, and
• a flue gas cooler configured to receive flue gas from a combustion and transfer heat from the flue gas to feed water in said heat recovery fluid circuit, and
• a waste heat accumulator configured to form part of said heat recovery fluid circuit and receive feed water via a waste heat accumulator feed water inlet, said heat recovery circuit comprising an inlet valve upstream of said waste heat accumulator in order to control the flow of feed water into the waste heat accumulator, said waste heat accumulator located downstream of said flue gas cooler in order to receive feed water heated by said flue gas in said flue gas cooler, said waste heat accumulator arranged to contain a mixture of water and steam produced by flashing the received feed water in order to generate flash steam, and
• said waste heat accumulator further comprising a steam outlet and a feed water outlet, said feed water outlet forming part of said heat recovery fluid circuit for return of feed water to the feed water main system via a heat recovery circuit outlet, and
• said heat recovery circuit further comprising an accumulator liquid inlet controller including a steam sensor for sensing the temperature and/or pressure of the steam in the waste heat accumulator in order to control a waste heat accumulator inlet valve so as to control the steam pressure within the waste heat accumulator in dependence of the sensed temperature and/or pressure.