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Friday 19 April 2019

mf fuels largest biomass boiler

Big bales, made by Massey Ferguson balers, are being used to produce energy and help heat 200,000 homes in Denmark

Jim Breen

Big square 4x4 bales made by Massey Ferguson balers produced in Hesston, Kansas, are playing a key roll in the production of energy at a substantial power station in Denmark.

Avedore 2, which is situated on the coast just south of Copenhagen, is reportedly one of the world's most energy efficient combined heat and power (CHP) plants. It extracts up to 94pc of the energy content of its fuel for electricity and heat generation -- meeting the heating demands of 200,000 households and supplying electricity to over 1.3 million homes!

The power station's biomass boiler plant is also the largest in the world.

Avedore Power Station is owned by Dong Energy. The company is the result of a merger between Dong, Elsam, Energi E2, Nesa and the electrical departments of two major utilities.

Dong Energy is active in every link of the energy chain -- from offshore production platforms in the North Sea, offshore wind-farms and power plants generating electricity and heat, through to the delivery of energy to the customer.

Avedore 2, which was commissioned in 2001, replaced a number of older coal-fired generating units in eastern Denmark, resulting in a 10pc reduction in carbon dioxide emissions. The power station was designed specifically as a 'multi-fuel plant', which allows it to use a number of different fuels from natural gas and oil through to a range of biofuels, including straw.

Last year, the plant consumed 172,000 tonnes of bales including rape, cereals and ryegrass from 500 different farms in eastern Denmark. Every day, Avedore 2 handles 65 lorry-loads of 24 bales. Currently these loads weigh about 12 tonnes, but with the increased density from the latest MF 2190 balers the payload is expected to increase by at least 20pc, further improving the efficiency of the operation.

The high volumes of biofuels consumed by Avedore 2 in its energy production helps the company to comply with the Danish Parliament's biomass action plan. This set a target of 600,000 tonnes of biomass to be burnt annually in eastern Denmark, with Avedore 2 alone accounting for more than a quarter of this target!

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The straw-fired biomass plant, which is the largest in the world, consists of a boiler, straw store, ash separator and a system for handling the bottom and fly ash. The straw store holds enough bales to run the plant for two to three days, with deliveries arriving from Monday until noon on Saturday, every week.

The whole biomass side of the plant -- cranes, straw lines and feeding system -- is designed exclusively to handle bale dimensions of 1.2m x 1.2m x 2.5m. "The higher density and heavier packages made by the latest MF 2190 balers will be of great benefit to us, helping to further improve efficiency -- simply because the straw lines will be able to handle more material," said Pernille Harder Andersen, information officer at the plant. The bale size choice also reflects years of experience from farmers and contractors baling straw for industrial and other uses.

The plant will accept bales with moisture contents up to 24pc and farms are expected to store them under cover until they are required. Bales are then transported to Avedore 2 on lorries stacked with 24 bales laid across the bed in two layers. On arrival, the trucks are unsheeted on a special gantry. Then the truck moves to the unloading area where the bales are weighed and ultra-sonic sensors are used to check the moisture content.

If the moisture content is OK, the operator, sitting high up in a control room, uses an over-head crane to lift off each layer of 12 bales in one go. He then stacks the bales in the storage area in a particular pattern, which is critical because from now on all the handling is carried out automatically.

Two special straw 'tables' feed the bales onto four straw lines that convey the MF 'Hesston' bales into the process. First job is to remove the strings, which are cut and stripped off before the bale feeds into contra-rotating peg rollers that loosen the material before it is blown into the boiler.

"It is actually very difficult to combust straw because its silicates are very corrosive. While it works very well now, it took quite a while to perfect the system and get it running this efficiently," Ms Harder Andersen added.

The steam generated by the biomass boiler is directed to the central turbine, which makes much better use of the energy in the fuel compared with using a separate steam turbine.

Integral

The biomass plant is, however, an integral part of Avedore 2's heat and electricity production and is one of three modules that also include a USC (Ultra Super Critical) plant and two gas turbines.

The USC is the 'heart' of Avedore 2 and comprises a boiler, steam turbine, generator and flue gas cleaning plant.

By increasing steam pressure and temperature to exceptionally high levels it ensures very efficient fuel use. This means Avedore 2 uses less fuel to generate one kilowatt-hour than older generators. It uses about half of the energy in the fuel to generate electricity compared with only 35pc fuel utilisation in older units.

The USC plant is connected to two gas turbines, each capable of producing 55MW as well as being linked to the biomass boiler that generates 40MW. Connecting all the systems together creates a synergy that means the total output is greater than all the individual parts.

This is what makes the facility one of the most flexible and energy efficient combined heat and power (CHP) plants of its kind in the world.

The gas turbines in Avedore 2 work as a 'peak load' facility, which means they are started up when there is additional demand for electricity and heat -- usually in the mornings and evenings.

Interestingly, one of the highest demands is on December 24 at about 4.30pm -- when Danish families are in the midst of Christmas festivities.



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