Biomass boilers - ecological effects

TECHNICAL ANALYSIS OF ECOLOGICAL EFFECT CONCERNING ENERGETIC POLLUTION LOADS DISCHARGERD TO THE ATMOSPHERE OBTAINED BY EXCHANGING COAL BOILER TO STRAW BOILER ON THE EXAMPLE OF ONE OF METALERG’S COMPANY BOILER-ROOMS. MADE BY INSPECTORATE OF ENVIRONMENTAL PROTECTION IN POZNAŃ.

Basing on presented materials and calculations Inspectorate of Environmental Protection in Poznań informs that modernizing heating systems consisting of changing RUMA 350 and ES-KA/S coal boilers (burning about 200 Mgr/r of coal) for EKOPAL type straw boiler with 0,5MW power (burning about 320 mG/r of straw) - basing on the instruction and information materials no. 1/96 Ministry of Environmental Protection, Natural Resources and Forestry titled “Emission of air pollutants from energetic processes of burning fuels” and informing materials provided by biomass straw boilers producer – MetalERG company, and the articles from addition to trade magazine Przegląd Komunalny from 2001 - lowers the emission of following types of pollutions:

 

Pollution type
Emission from coal combustion (kg/r)
Emission from straw combustion (kg/r)
Ecological effect (kg/r)
reduction %
 Sulfur dioxide  2144  256  1888  88
 Nitrogen dioxide  300  205  95  32
 Carbon monoxide  9000  1920  7080  79
 Total dust  3900  2218  1682  43

 Total reduction of carbon dioxide (CO2) emission from straw burning – during combustion of the straw no more CO2 is emitted than it was taken from the atmosphere by straw during its growth.

According to this, the following invest took part in developing an measurable ecological effect proved by numbers provided above. Achieving those effects is possible in case of combusting wheat straw “gray” with humidity at 15-18%.

Fresh straw consist significant amounts of chlorine, and its combusting when humidified causes lowering heat efficiency of boiler. According to this fact straw bales should be stored under the roof few days before burning.

Pollution gases emission from boiler-room with one EKOPAL RM 10 type boiler with 65 kW of power compared with pollution gases emission from coal boiler with the same power (following sources from Denmark):

afterburns components
Heat production = 65kWh Final effect
    Coal combustion
Straw combustion
for 65kWh
for 130MWh
(2000h per year)
1
2 3 4 5
6 7 8
9
10
Component

Weight Volume
kg/m3

Coal consumption
kg/h
Emission in afterburns
m3/kg
Emission in afterburns
kg/h
Straw consumption
kg/h
Emission in afterburns
m3/kg
Emission in afterburns
kg/h
Emission lowered kg/h Emission lowered kg/year
CO2 1,977 10,00 1,0387 20,53 15,00 0,73349 21,75 -1,22 -2440
SO2 2,9267 10,00 0,00683 0,1998 15,00 0,00109 0,04785 0,152 304
Dusts 2,03 0,46 1,57 3140

Assuming operating time of boilers – 2000h per year, and average coal and straw using per hour:

-        Total amount of CO2 emitted in exhausts during one year: for coal – 41016 kg/year; for straw – 43500 kg/year. As you can see the amount of CO2 emitted to the atmosphere by straw burning process is higher but in case of straw the CO2 amount is just refunded to the air for the CO2 taken by the straw during its growth. To sum up, the amount of CO2 emitted from straw combustion did not increased total amount of CO2 in the atmosphere in contrast to the coal combustion with added 41016 kg of CO2 to the atmosphere and this have effect in increasing the greenhouse effect.

-        Total amount of SO2 emitted by coal is 399,6 kg/year. Total amount of SO2 emitted from straw combustion is just 95,7 kg/year. According to this coal is emitting 303,9 kg/year more SO2 to the atmosphere than straw.

-        Total difference in emitting ashes is 3140 kg/h against coal.