Wood chips
 

Gasification of wood chips

Gasification is an alternative to traditional combustion plants as it is possible to generate more efficient electricity in small plants and thereby reduce the fuel input.

Gasification is a reliable and clean energy technology that can turn biomass or any material containing carbon into synthetic gas. This gas can then be used in a gas engine for the production of electricity and heat. A significant benefit is that the equipment is compact, which enables a plant to be built in small communities where electricity, steam or heat is needed.

Our experience exceeds 120,000 operating hours

Since 1989 we have been accumulating knowledge about the efficient operation of a gasification plant.

In 1993 we established a demonstration plant in Denmark, the Harboøre gasifier plant. In 1997 the gasification process was considered commercial. Since then the plant has operated 8,000 hours per year, making it a global leader in the operation of a gas engine combined with a gasification plant.

The Harboøre gasification plant is in operation all year round. It burns bio-oil when the gasifier has its main renovation one week per year.

Our expertise is renowned; we have supplied gasification technologies for three plants in Japan.

Small gasification plants can obtain a high electrical efficiency

Gasification is an alternative to traditional combustion plants as it is possible to generate more electricity than with the existing solutions based on steam in small district heating and industrial plants.

In small combustion systems (up to10 MWe), energy output is limited to production of hot water (e.g. for district heating) or steam for relatively low-efficiency processes. In gasification systems efficiency may exceed 30%.

The technology plays a key role in the development of CO2-neutral energy supplies. Because it emits less CO2 and NOx pr.-produced KWhe, a gasification plant significantly reduces the environmental impact compared to traditional technologies. And because less fuel is needed, the whole production chain is smaller. The plant can be placed decentralised to minimise losses in the grid network and secure local workers’ jobs for sustainable energy production. 

Profitable feed-in tariffs for smaller plants

Feed-in tariffs, or renewable energy payments, vary from country to country. But generally governments support smaller plants, which are local and frequently use locally produced fuel. This by itself is more environmentally sound since transport is closer.

The rapid turn-down ratio is suitable for the electrical grid of the future

Biomass plants are designed to deliver a certain amount of output. Turning that down, or feeding the plant less fuel, can be difficult as it gets harder to stay within emission limits. With gasification it’s easier to stay within the limits even when you turn down the amount of fuel. This is especially important during times when you need less electricity. The rapid turn-down ratio is very suitable for the electrical grid of the future. Anticipating that much of our electricity will come from wind energy, a gasification plant can secure electrical supply to the grid, when the wind is not blowing.

No specialised pre-treatment of fuel is needed

The great advantage to this technology is that you do not need to pre-treat your wood chips. Our fuel is primarily wood chips and comes directly from the woods where it is chopped. This saves time and money because specialized treatment such as drying or sorting of fractions is unnecessary.

Tailored gasification technology to meet your needs

We can tailor our gasification technology to suit several different concepts, e.g.: power plants, combined heat and power plants (CHP), combined cycle gasification, heat, and syngas. The latter can be used as fuel for an external superheater at a waste-to-energy plant (WasteBoost™). This concept is designed to increase steam parameters and thereby electrical efficiency. 

Today we market a CHP design of a 2MWe plant with a power efficiency of 28 %. This concept is based on virgin wood chips coming directly from the woods without any pretreatment or drying.

Capital investment cost figures for gasification plants are relatively high compared to traditional steam cycle concepts. However, where high feed-in tariffs are provided, an evaluation over a period of Total Cost of Ownership (TCO) gives the optimal feasibility for the investor. This is mainly due to the much higher electrical efficiency.

Capital investment cost figures for the “electro-mechanical” part of the plants are approx. 13,500,000 EUR for the 2 MWe design. Add approx. 20% extra cost for the turnkey prices.

This cost level is only feasible in a few countries, mainly in Europe, where you have a high tariff for power and have the possibility of selling the heat. Depending upon your required payback time and fuel costs, etc., this will form the basis for the evaluation for the TCO.

How gasification works

In the gasification process, the unhomogeneous biomass such as wood (bark, branches, leaves, woodchips, etc.) goes through a thermal chemical process using moisturised air.

The moist biomass is fed at the top and descends though gases rising in the reactor.

In the upper zone a drying process occurs, below which pyrolysis is taking place. Following this, the material passes through a reduction zone (gasification) and in the zone above the grate an oxidation process is carried out (combustion). To supply air for the combustion process and steam for the gasification process, moist, hot air is supplied at the bottom of the reactor.

Combustible gas at a low temperature is discharged at the top of the reactor, and inert ash from the heat-generating combustion process is extracted from the reactor bottom through a water lock.

The process breaks down the unhomogeneous biomass to the molecular level and converts it into a homogeneous fuel: synthetic gas (syngas).

The syngas can be used to create a variety of valuable products or you can burn it in a gas engine, which allows you to produce more electricity than any other available technology. The flue gas created in the process can be used to produce steam or heat water that can be provided to a district heating grid.

Our fully automatic gasification plants can save labour cost

Gasification plants from us are fully automatic and require minimal monitoring. This means that the operating and maintenance costs can be kept at a very reasonable level. Our demo plant at Harboøre, Denmark, is in unmanned operation evenings, nights, and weekends and to date the gas engines have been in operation for more than 100,000 hours, which is considered outstanding. Because it’s an unmanned operation, you save labour costs.

Harboøre biomass gasification plant

Residues from gasification: extremely low unburned carbon

The ash produced in the gasification process makes up just 1% of the biomass that is fed into the plant. In this ash there is very low TOC (Total Organic Carbon) which means that there is no energy loss. The ash is so pure that it can be used as fertilizer on farming fields.

As with all our technology, our gasification process is highly reliable

The water produced in the process is cleaned of tar which is converted into bio-oil. The bio-oil can be stored in a tank so that when the facility is closed down for revision you can still produce energy and provide the community with heat and electricity from biomass instead of being forced to supplement with fossil fuels.

The bio-oil is also useful in times of special need, during a very cold winter, for instance, when you need more hot water than usual for the district heating grid.

This makes our gasification plants extremely practical as well as reliable.

Read more about the Harboøre plant

For more information please contact our gasification specialist Robert Heeb, (+45) 7614 3596.Gasification process illustration

Process illustration of a gasification plant.

Gasifier reactor

The gasifier.