INTEGRATION OF SENSIBLE AND LATENT HEAT RECOVERY FROM THE EXHAUST GASES OF A WOOD FIRED BOILER IN POWER GENERATION

Ziel

To demonstrate that a CEECON three element condensing economiser can be developed from natural gas usage to successfully operate on flue gas from wet wood fuel combustion on a continuous basis to the reliability standards demanded in a power plant application. To establish the economiser can be integrated into the boiler combustion air, flue gas and condensate systems without undue problems and parasitic load implications. To measure the improvement in plant efficiency gained by the integration of the condensing economiser and establish any parasitic loads. To reduce the flue gas moisture load and reduce the environmental impact of the stack plume.

The generator plant is a conventional high pressure steam system with a boiler specially designed for wet wood combustion, and a condensing turbine with a shell and tube vacuum steam condenser cooled by cooling tower water to give a turbine exhaust condition of 40 deg. C, and an electrostatic precipitator for flue gas fly ash removal. The plant is designed to generate 10 MW nett electrical from the combustion of 25 tonnes per hour of 58% moisture fuel at a conversion efficiency 25% thermal to electrical, with a boiler flue gas exit condition of 150 deg. C with 235 gm/kg dry gas moisture.
Condensate from the vacuum steam condenser is heated to 90 to 95 deg. C by bleed from a tapping on the turbine to temper it before entry to the de-aerator operating at 105 deg. C. Although no heat is lost in this process, the bleed steam amounting to about 10% of total steam flow, could be used to generate electricity if allowed to pass through the LP wheels of the turbine to its vacuum exhaust.
If this bleed steam could be replaced by another heat source, the amount of power produced by the LP end of the turbine would increase and so less total steam production would be required to generate the same power. Additionally, the temperature of the combustion air for the burners directly affect the combustion temperature of the wet fuel. Pre-heating the air increases the combustion temperature which benefits the heat transfer process within the boiler and increases boiler thermal efficiency.
The exit flue gas contains a very high level of moisture which would create a very significant plume if not condensed. The equipment to carry out this duty to improve the environmental impact of the plant is both costly and power consuming, which adversely effects the overall economics of the installation.
The CEECON Economiser replaces bleed steam using firstly a condensing section to heat the water to the flue gas moisture dew point, and then an intermediate circuit sensible heat sectionto upto over 90 deg. C. The water entering the condensing section is boosted substantially in circulation by a recirculation plump which pumps through an intermediate heat exchanger to transfer heat to the combustion air via close approach finned tube heat exchangers. The combustion air is thus heated to within 5 deg. C of the flue gas water dew point. This increases the combustion temperature in the boiler by about 40 deg. C, which aids the combustion process and heat transfer within the boiler besides directly reducing the heat required from the fuel to carry out this heating during combustion.
The reduction in the steam generation requirement due to condensate heating amounts to appproximately 3% whilst the improvement in nett thermal efficiency produced by pre-heating the combustion air is approximately 2.3%. Therefore, the boiler heat load is reduced by 3%, which is provided by a combustion system working at 2.3% greater nett thermal efficiency.

Programm/Programme

ENG-THERMIE 1 - Programme (EEC) for the promotion of energy technology in Europe (THERMIE), 1990-1994

Thema/Themen

2.3 - INDUSTRY

Aufforderung zur Vorschlagseinreichung

Data not available

Finanzierungsplan

DEM - Demonstration contracts

Koordinator

Balcas Ltd

EU-Beitrag

Keine Daten

Adresse

Laragh
BT74 2FQ Enniskillen
Vereinigtes Königreich

Gesamtkosten