Wood Chip Gasifier and Wood Gas Cogeneration

Raw material Wood chips, up to 300 kg/h
Generated power 250 kWe
Generated heat 580 KWth (77°C / 70°C hot water loop)
Duty cycle 7512 hours per year (160 hours in operation, 8 hours maintenance and cleaning per week)
Total production Power: 1878 MWhe/year
Heat 4357 MWhth/year

Principle and Visualization of the Technical Equipment

The biomass gasification process (using wood chips) occurs in a gasifier that generates wood gas. After gasification the resulting wood gas must be filtered to remove tar and water and can then be used in an ordinary combustion engine and generator to cogenerate both power and heat.

The equipment itself is packaged into modular containers and can be multiplied as 250 kW, 500 kW, 750 kW and 1000 kW of electric power.

Standard Rates of Consumption for Raw Materials and Utilities

Standard rates of consumption for the primary product - power

Raw material Consumption per 1 kWh export Unit
Dry wood chips 0.90 kg
Internal power use 0.1 kWh
Propane 0.001 kg
Diesel 0.001 l
Well water 15 kg

Layout of the Equipment

The equipment is housed in 4 containers. The equipment will be installed in steel transport frames (shipping containers without side walls and doors but with integrated rigging cleats used to ship the equipment and to anchor to a prepared concrete base with anchoring eyelets) instead of standard steel structures. On site these steel frames will be used reassemble the machinery and equipment. Small gaps must be maintained between the equipment and must be carefully resolved due to the high temperatures of the fittings and piping and the bridging that must take place; each individual piece must be aligned along the gap itself and flexible connections, oval openings in anchors, friction pads, etc. must all be used to ease the equipment's installation in its working position. The package plant principle is applied.

The container will be ventilated through the reinforced steel frame used to hold equipment installed in working positions and will contain all work platforms, electrical panels and measurement and controls equipment. Individual pieces of equipment will be connected with piping. All equipment must be cleaned and blanked before moving into the operating position in order to prevent dust from entering inside and must be secured from moving side to side in the frame.

If the container will be erected into a vertical position, all equipment must be locked down during transport to allow transportation in a position other than the operating position.

Three containers will be horizontal and one container will be vertical on site. A container will house two floors with the upper floor limited by a shipping height of 2.6 m with taller equipment either slanted to fit or moved to a lower position. Freight trucks will have access from both sides of the containers on site. Each container will be equipped with stairs, emergency ladders, emergency lighting, fire fighting equipment and a fire alarm.

Each container will contain an electrical panel and an interface unit for connecting lateral communications to the control computer in the control centre.

A fire alarm system will be included in the project along with a design layout for for fire-rated walls in areas with high fire hazards.

Disposal of Liquid, Gas and Solid Wastes

Solid Wastes

Solid wastes generated by the gasifier during regular operations are caused by dirt and stones in the processed raw material. Uncontaminated sludge from the dryer will be removed during shut-downs to a collection drum and then turned over for landfill disposal. Cinders containing heavy metals are separated on the grates and such content primarily depends on the processed raw material. The content of such heavy metals will be lower in coarse ash or cinders than in the fine ash; some heavy metals migrate with the wood gas. In general this waste can be spread on fields depending on its composition; if not suitable for use in fields, the waste can be disposed of in a landfill. The use of wood ash as a fertilizing agent helps maintain productive biomass soils.

Cleaning work during shut-downs is only expected in a few parts of the system and the waste that is generated can be incinerated; this waste is moved to a transport container and disposed of in a solid waste incinerator.

Liquid Wastes

Liquid wastes are generated during regular operations by the condensation of moisture content in the raw material. The water contains ash and the expected annual quantity is 400 m3. The dissociation of salts occurs in the gasifier, for instance K2CO3 into CO2 and K2O, which sublimate and create a fine powder that is water soluble and captured in the wash water, which creates an alkali environment that later reabsorbs CO2 from the gas, thereby reconstituting the original K2CO3. CaO, Na2O, K2O, Cl, Zn, As, Cd, Co, Cr, Mn, Pb, Se, and Hg all behave in a similar manner. The presence of these metals is possible if waste wood that was chemically treated or painted will be incinerated and these wastes are always conditioned by such risk. In general the liquid wastes can be sprayed on fields after a check to ensure the contents are inert. The composition remains the same if identical raw materials are used, which means analysis does not need to be repeated if the same raw material from the same source is used.

Hazardous waste analysis must be completed before waste is turned over for landfill disposal or to a MCHB (mechanical, chemical, biological) wastewater treatment plant.

Gas Wastes

Gas wastes are generated during regular operations in the form of exhaust containing SO2, which has a low concentration in the raw material, and NOx generated by wood gas combustion in the motor.