Panorama Editorials Archive

Editorials Archive

Biomass Intake for Power Utilities and CHP Plants

Biomass Intake for Power Utilities and CHP Plants

The world’s demand for primary energy is predicted to increase by some 36% between from the 2008 level through to 2035 using the New Policies Scenario developed by the International Energy Agency using data provided by contributing countries.

Sustainability obligations are driving almost every major electricity utility and process steam generator worldwide to address the issues surrounding their plant carbon footprint within the industry published commitments and governmental aspirations to reduce in total greenhouse gas generation. With coal fired power plant representing around 40 percent of man-made carbon dioxide emissions there is a considerable incentive to incorporate Biofuels into the total fuel mix to reduce the plant carbon footprint. The OECD expects biomass usage for energy production in power plant to more than triple within the next two decades. Depending on local availability biomass already has an important share in electricity production especially in countries with a large timber industry as for example Austria (20%), Norway (40%) or Sweden (70%). However, the majority of recent biomass power plant projects are aimed to gain greater independence from fossil fuels and help industry to reduce their carbon footprint.

Biomass fuels (solid Biofuels) are defined as originating in living or recently living organisms and in general are considered carbon neutral as the carbon released when they are burnt to generate steam is offset by the carbon absorbed by the organism during its lifetime. Consequently when Biomass fuels are added to the solid fossil fuel mix at a coal burning power plant the addition of the Biomass offsets a similar volume of coal equivalent thus reducing the plant carbon footprint whist maintaining the same electrical output level.

However, this calculation is complicated by the inducements offered in many developed economies known as the Feed-In-Tariff generally for smaller projects; this is an artificially high payment per kWh., or compensation rate, for power generated from renewable resources such as Biomass. This system of incentives based on carbon reduction or renewables obligations certification (ROC) is employed extensively and is used to justify the financing and construction of many existing Biomass power plants with many more very substantial ventures in the planning, combined heat and power (CHP) projects being particularly interesting and energy effective.

Biomass fuels vary considerably including such as Wood Chip, Forest product wastes, wood pellets, agricultural wastes, animal litter, sludge including sewage sludge and combustible fraction of garbage that cannot be recycled or refuse derived fuels (RDF) are only a few examples. With present oil prices it is even economically viable to create biodiesel from municipal sewage although the process is presently at the research stage. One of the key factors in all of these examples is the relative location of the material source and the power plant and the requirement to ship the biomass material often by truck, rail, barge and ship demanding logistical facilities for the environmentally acceptable transfer between each mode of transport.

For power utilities CHP solutions may be difficult since, with present public attitudes, it is often not viable to build the biomass power plant close to centres of population. Locating the CHP plant close to a dedicated industrial site is generally more viable. Invariably then a range of transportation solutions are required and the handling systems that support the logistics must be tailored to suit the Biomass characteristics.

One such proposal is the new CHP plant to be built for Tulliss Russell paper maker the located at the Markinch in the Fife region of central Scotland. Tulliss are a very long standing client of B&W Mechanical Handling Ltd. having taken a SamsonTM surface feeder back in 1987 to intake coal for their steam plant. For this new project RWE npower renewables is working in partnership with Tulliss Russell to generate steam and electricity for the paper plant from a new biomass facility. The new Biomass plant, which will be the biggest of its kind in Scotland, will have an installed capacity of 50 megawatts and will replace the existing coal-fired power plant at Tullis Russell and should be complete in 2012.

It is anticipated 17 mW. will be used by the paper plant and the balance of the power generated will be sold to the grid benefitting from the Renewable Obligation (Scotland) scheme applicable to Biomass generation, CHP schemes that use a renewable energy fuel earn a premium on each MWh of electricity produced under the Renewables Obligation (RO) mechanism.

Using carbon neutral Biomass fuel the plant will reduce Tullis Russell's Markinch site carbon footprint by 72%, helping to reduce the carbon emissions at the paper maker by around 250,000 tonnes per annum.

For AUMUND, through their UK subsidiary B&W Mechanical handling Ltd., the contract for Tulliss Russell includes four identical SamsonTM surface feeders to intake and store Biomass from road vehicles providing a controlled discharge rate to the ongoing conveyor installation. The concept is very similar to that illustrated herein installed for Electrabel-SUEZ in Poland handling Agri-Biomass.

Renewable fuel CHP facilities that supply heat for industrial processes are a key component of the UK’s low-carbon strategy. The UK Government expects to see 10GWe of CHP capacity installed by the end of 2011 and to be approaching 14GWe by 2015. This compares to an estimated 5.5GWe in 2008, which then accounted for around 7% of the UK’s electricity.

This Scottish project is not the only application for RWE, another new SamsonTM surface feeder will be supplied to RWE Kraftwerk Ibbenbüren to intake Meat and Bone Meal for co-firing along with mainstream coal usage. In Europe, some MBM is used as ingredients in pet-food although the levels were substantially reduced after it was linked to the development of Mad-Cow disease in cattle and now the vast majority is used as a fossil-fuel replacement for renewable energy generation.

Meat and bone meal has around two thirds the energy value of fossil fuel such as coal; the UK in particular widely uses meat and bone meal for the generation of renewable electricity.

Chicken and Turkey Litter:

The volume of poultry reared worldwide is enormous and fast approaching a total of over 80 million tons annually with a growth rate of over 5% with the greatest expansion in demand in China... Naturally this generates a vast volume of litter, which is generally a mixture of droppings and bedding which may be straw or wood shaving or similar absorbent materials. Litter may be simply recovered using a small skid steer loader and removed from the farm using conventional tipping trucks, generally fitted with an sheeted enclosure to minimise odour escape, the smell is intense and represents a major issue for the disposal of the litter. Litter has a calorific value approximately 50% that of coal and is a viable fuel for power generation and is classified as Biomass and carbon neural.

Within the UK a number of dedicated power plants were built from the mid 1990s including an important large scale station close to Thetford in the East of England, the most intensive area for poultry rearing. This is a 38.5 mW. station and burns 450,000 tons of litter annually delivered by tipping truck from local farms to a total of 6 intake lanes each equipped with SamsonTM feeder units by AUMUND. Each intake lane comprises a SamsonTM feeder to receive the litter in bulk and provide buffer storage plus a controlled discharge rate to the following disk screen. The screened material is collected beneath the rotating disks by a second SamsonTM feeder which discharges to a common collecting conveyor which receives screened litter from each intake lane. The screened material is transferred by conventional troughed belt conveyors to a main storage area. In total 12 SamsonTM feeder units were supplied for this project, six units for intake and six sub-screen feeders.

Chicken and Turkey litter can be extremely slimy and prone to sticking on almost any surface and certainly will not flow down chutes nor can it be extracted from conventional hoppers. In these circumstances the wide belt SamsonTM solution with vertical hopper walls proved ideal, and, combined with a levelling blade to even the material bed depth at the discharge, gave the required uniformity of output to enable the rotating disk screen, by Lubo of Holland, to function effectively and remove oversize and tramp materials. Furthermore the SamsonTM feeder may be inclined to the discharge offering a reduced excavation depth or minimum truck ramp height to reduce the cost of the associated civil works and foundations.

For many years these attributes have made the SamsonTM as a concept ideal for the intake of fossil fuels and pet-coke but it is these benefits that also make the SamsonTM ideal for almost any application where Biomass is received from road or rail.

Agri-Biomass:

Scottish and Newcastle Brewery (Heineken) have chosen the SamsonTM Surface Feeder to intake mainly spent grain from their brewing process along with wood chip and prunings from local orchards. Similar systems are installed at their Manchester and Tadcaster breweries, each new CHP plant will generate around 4.7 mW. fuelled entirely by Biomass providing around 60% of the steam demand and all of the on site electricity reducing the total carbon footprint for both sites by some 30,000 tons of CO2 equivalent when fully operational.

In addition to the benefits of Biomass steam/power generation, by pressing the spent grain on site Biogas is released which will be used to fuel a CHP engine offsetting altogether about 15% of the total gas usage. The spent grain also has high phosphate content so the ash from the biomass furnace will be sold as fertiliser... A Win-Win-Win solution...

A more recent example B&W Mechanical Handling Limited has been awarded a contract by Mostostal Zabrze Holding S.A. to supply a new biomass fuel handling reception system to the Polaniec power plant in Poland. Polaniec is part of the Electrabel-SUEZ Group and is the fourth largest power plant in the country.

The project includes four SamsonTM Feeder units which together form a new Biomass intake system discharging via transfer conveyors to the existing main coal handling plant. Each Samson Feeder has been rated to receive up to 300m3 per hour from 30m3 capacity tipping trucks unloading between 6 to10 trucks per hour.

The biomass material includes mixed pellets, sunflower seed briquettes, straw, dried fruit and cherry stones plus no doubt other exotic materials that may be available in the future. To handle such potentially hazardous materials the SamsonTM was supplied with ATEX certification achieving Zone 21 internally at the discharge and the highest Zone 20 rating at the entry section.

Sewage Sludge as an Alternative Fuel:

Whilst the other fuels we have mentioned here are difficult to handle sewage sludge is in a wholly different category with as low as 20% dry solids content this materials sticks to everything and flows down nothing.

Typically the liquid sewage will be treated and filtered and the resultant solids de-watered in a filter press producing sludge cake that may be easily transported to common pelletization plant. Normally sludge cake will be hauled out of the treatment plant and dumped in landfill, this is not sustainable and now with additional treatment, such as pelletization, the sludge is easier to handle and economical to transport and use as an alternative fuel. Of course this material is in plentiful supply and, with expanding urbanisation and more stringent standards on pollution of rivers and coastal areas increasing volumes are now effectively treated by using some kind of wastewater biological treatment plant.

Burning this material through a power plant or cement kiln has the added benefit potentially deleterious and carcinogenic compounds within the sludge are destroyed resulting in measurable health benefits compared to dumping or other means of disposal that allows these compounds to remain in the environment.

Since 1993 B&W Mechanical Handling Ltd. have supplied SamsonTM intake and storage solutions handling de-watered sludge received by tipping containers at central processing facilities. From the SamsonTM intake the sludge may be conveyed on simple troughed belts, the B&W Kleen-Line solution being most appropriate, or it may be plasticized and pumped using a progressive cavity style pump and conventional steel pipe-work thus simplifying the conveying route. For larger plants a special version of the SamsonTM is available with extended holding capacity to 200 tons or more acting as a live storage from which the material may be plasticised and pumped to the pelletization process or directly into fluidized bed or multiple hearth style furnace.

Conclusion:

From these typical case studies it is clear the characteristics of Biomass Fuels varies significantly from light and friable materials such as woodchip and untreated sawdust through to heavy, wet and sticky sludge such as sewage and chemical residues.

Receiving, feeding, handling and storing these materials is a real challenge, particularly in continuous process applications where availability 24/7 is mandatory. Delivering reliable and efficient solutions requires both ingenuity and experience applying existing proven technologies in new extraordinary applications.