Jonathan O'Reilly

USE OF CHP AND RENEWABLE SOURCES OF ENERGY FOR INDUSTRIAL BOILERS

Introduction

Industrial facilities in Ireland contribute highly to the overall proportion of tonnes of CO2 emitted in Ireland each year. A large amount of this is developed because steam production. Steam is essential in many industrial processes where it is used for heating or evaporating off liquids. These industrial processes that contribute significantly to Ireland's CO2 footprint include dairy processing plants and cement manufacturing plants.

With the current economic situation output from cement manufacturing plants is not likely to be increasing production in the immediate future. However there is a planned increase in milk output from farmers in the next several years. The plan outlined in a government food harvest 2020 report for a 50% increase in milk production. The exact details of how this increase in processing capacity will come about is as of yet been decided upon but what is clear is that there will be a large increase in steam production across the entire Irish dairy industry. [1]

How will this steam be produced. Steam is traditionally developed in boilers, which are feed by oil or gas. The oil or gas is burned and the heat is used to turn water to steam which is used in the industrial process. The steam is then used either to generate electricity or used directly for the industrial process, typically heating purposes. There has been a turn in recent years with worldwide and within Ireland to a degree to install more environmentally friendly ways of generating steam. I have included two diagrams below to show what a industrial boiler looks like

This particular boiler passed the hot gasses over water three times to increase the area of heat transfer between the water and gasses, most modern plants will either be 3 or 4 pass systems. [2]

This picture is to give people who are unfamiliar with an industrial boiler an idea of what they look like, as a reference.

Many operators in Ireland including Kerry Co-op and Dairygold have started to install CHP units in their factories in an effort to reuse some of their waste heat and to reduce their carbon footprint. The need to be able to resupply the electric back into the national grid is essential in the economic viability of any such CHP unit. From the prospective of the operator of the national grid someone supplying in electricity from a CHP unit can provide a more constant supply than from say a wind farm on the west coast of Ireland as there need not be the peak and trough as a CHP plant can stay producing and will only shut down either for maintenance or lack of feedstock.

For the most part though in Ireland boilers and CHP units are still run on fossil fuels, mainly oil and gas (usually gas if they can get a feed from the national gas supply, as gas boilers tend to be easier to startup and shut down and require less maintenance). There are some plants that are running boilers and CHP units on biomass, e.g Grainger's Sawmill in Cork ( see case study 2). Within Europe their is a growing trend to move towards these alternative energy sources for use in an industrial steam generation.

So what are these alternative energy sources??! Glad you asked!!! [3] [4]

Woody Biomass

• clean wood

• recycled wood

• forest residue

• willow/miscanthus

• bark

Agricultural Fuels

• straw

• grains

• chaff

• hemp

• olive residue

• citrus pulp

Waste Fuels

• sewage sludge

• manure

• rubber tyres

• leather waste

• cardboard rejects/cut-offs

• plastics

Other Fuels

• meat and bone meal

• animal and vegetable fat/oils

• peat

This webpage will examine the most promising of these technologies and see which if any could be put to use in an industrial context in Ireland.

BIOMASS FEEDSTOCKS

The use of biomass feedstock to generate steam or heat have been used on a small scale for several years. In Ireland there has a been lack of take up in an industrial context. There has been more of a take up on small scale boilers for domestic and other type of residential usage ( say hotels and offices) and within Europe there has been more of a take-up in biomass feedstock for industrial boilers.

Biomass feedstock all all around us and would reduce Ireland dependency on foreign fossil fuels. Ireland is more dependent on fossil fuel imports due to our lack of fossil fuel production. The advantages with fossil fuels is that they are easily transported and easy to use and typically have high calorific value. Presently the boiler that use fossil fuels as a feedstock are cheaper to install and operate.

Disadvantages of biomass feedstocks ( especially timber pellets)

• the timber pellets consume oxygen and emit carbon monoxide, this can be a health and safety concern, indeed there have been fatalities on a cargo ships carrying timber pellets where two seamen died due to lack of oxygen below deck

• there is an inherent fire hazard with burning wooden pellets. in some case the storage bins caught fire due to the that on the conveyor belts carrying the pellets to the burn taking heat back to the storage bin

• the dust in the storage bin can give rise to dust explosions

• also if water happen to get into the pellets they will expand rapidly causing structural damage to storage units

• some biomass feedstock can release a lot of ash, if this ash is released on the tubes in a boiler it will degrade heat transfer across the surface of the tube which could drastically impair the operational efficiency of the boiler

These issues combined with a lack of meaningful governement incentives in Ireland have lead to a lack of widespread take up of commercial biomass boilers. There is also a limited amount of wood pellet suppliers currently in Ireland, especially when compared to oil and gas suppliers.Or at least this is the view within industry. Even though it is imported there are a variety of suppliers within Ireland. A manufacture of say milk powder or cement does not want to spend a few million on a new biomass boiler only to worry about the security of supplier of feedstock, especially if the alternative if financially more appealing!

In the past several years a technique called co firing has been developed. Co-firing of biomass fuels in mainly coal-fired units, and thereby replacing part of the coal, has been adopted worldwide. This is seen as a short-term solution to exchange traditional fossil fuels such as coal and fuel oil, with a sustainable large scale of solid and liquid biomass types, like wood pellets or palm oil, in order to reach environmental incentives. Currently, over 234 units have either tested or demonstrated co-firing of biomass or are currently co-firing on a commercial basis. Coal is often replaced by biomass in pulverized coal plants up to 30% biomass, as in Belgium, Canada, Denmark, Finland, The Netherlands, Sweden, United Kingdom and the United States. Some countries adopt a mixture of biomass and fossil fuel in dedicated boilers. Blends of biomass and fossil fuels are utilized commercially in bubbling and circulating fluidized beds in countries as for example Austria, Finland, Sweden and the United States.

This however may not be applicable for many Irish industrial situations. However it may be useful for any steam generation unit that is still using coal as there would be less modifications required than a oil or gas installation. Also there are issues surrounding the security of supply of the biomass feed itself. It is not yet available in large amounts required for commercial industrial installations. Government guidence or incentives are required to overcome this issue. [3]

Agricultural Fuels

Agricultural fuels are have yet to be incorporated fully into the industrial mainstream for steam generation. Some countries in Europe most noticeable Denmark has lead the way in using indigenous biomass materials such as straw by using specific government policy to promote the use of these substances. The issue with biomass it that to required a significant amount of land area to grow the crops. In Ireland it is straw that would be the most common fuel source available and even this is not currently that readily available. on personnel evidence from living on a farm myself there has been a growing lack of straw for sale for animal bedding in recent years. There would;d need to be a dramatic increase in tillage production in Ireland for be able to use straw for fuel. this might change in the future with the recent talk of a sugar beet/grain bio-ethanol plant begin build ( straw is a by product of grain) however this is several years down the road.

Waste and other sources of fuel

these other sources of fuel in use for steam production are still a long way from being use in a industrial context. while there are several trial plants around Europe [3] the majority are some form of co firing plants as described in the above sections. the cost implications of installing these in place of a oil/gas burning boiler are prohibitive.

CHP- Combined Heat and Power Units

CHP is an energy efficiency technology. It provides a means to substantially reduce fuel, consumption without compromising the quality and reliability of the energy supply to consumers. Therefore it provides a cost-effective means of generating low-carbon or renewable energy. The energy savings delivered by CHP are underpinned in law and through supporting regulations. The EU Cogeneration Directive defines CHP as delivering minimum levels of primary energy savings, with savings of 10% required for most CHP capacity.[5]

The efficiency benefits of CHP go on to provide a range of wider advantages. Delivering the same energy more efficiently, using less fuel in the process reduces energy costs, enhances security of energy supply and helps mitigate dependence on imported fuels.

The move towards a lower-carbon future CHP also presents the opportunity to secure cost-effective reductions in CO2 emissions. The scale and cost of these savings will of course vary with respect to the scale, fuel and type of CHP plant, and in relation to the benchmark that is being used for comparison

Today’s CHP systems are based predominantly upon existing, proven power generation technologies: steam turbines, gas turbines and reciprocating engines used the world over to generate energy. This use and adaptation of existing technology not only contributes to the relatively low cost of CHP, but also ensures that it is a proven and reliable technology, capable of delivering an immediate impact in transforming our energy system.

Benefits of CHP

CHP provides the following direct benefits:

· minimum 10% energy savings, but often much higher

· cost savings of between 15% and 40% over electricity sourced from the grid and heat generated by on-site boilers

· minimum 10% CO2 savings for good quality natural gas CHP in comparison to conventional forms of energy generation

· high overall efficiency – up to 80% or more at the point of use

· additional guarantee of continuity in energy supplies for operator & consumer

· proven and reliable technology with established supplier base [6]

These in turn deliver a range of beneficial outcomes:

· a reduction in the cost of energy, improving the competitiveness of industry and business,

· enhanced security of supply, making energy go further, through more efficient use of fuel – regardless of whether the fuel is renewable or fossil

· increased flexibility and reliability of energy supply, both nationally and locally – as CHP can complement and enhance other forms of energy generation

· flexible and responsive heat supplies – the thermal energy (heat or cooling) produced by CHP can be easily stored and later delivered to meet demand

· reduced overall demand from centralised, such as large scale coal or gas fired power stations – thus reducing stress on the electricity grid

This diagram is for a biomass CHP plant. Its operation is fairy close to that of a fossil fuel burning CHP unit apart from the feed system to the burner. [7]

Case Study 1

British Sugar’s Wissington site in Norfolk UK is the largest sugar beet factory in the world and the most efficient factory in Europe. The site processes over 400,000 tonnes of sugar each year.

a highly efficient CHP plant commissioned at the end of the 1990s. The CHP plant provides a low cost source of energy for the facility and has, therefore, been a significant enabler to the expansion and diversification of the sugar factory.

This includes for example a modern biorefinery that produces 55,000 tonnes of renewable bioethanol per year. Heat recovery helps to significantly minimise the carbon footprint of the process. The site also hosts one of Europe’s largest glasshouses. This uses significant volumes of low grade heat and even the CO2 gases from the CHP plant to help grow over 80 million tomatoes each year (about 10% of UK demand).

The 70 megawatt (MWe) capacity CHP plant also meets the steam and electricity needs of the sites core sugar production operations and is able to export some 50 MWe of additional low-carbon electricity back to the local network. This is enough power to meet the energy needs of 120,000 people. Performance of the CHP plant itself was also recently augmented by the addition of a multimillion pound water injection system which boosts output from the gas turbine.

This highly efficient husbandry of resources – be it sugar beet, to energy through even to CO2 – combined with environmental awareness and responsibility, not only ensures that the carbon footprint of the site is minimised, but also helps preserve and enhance the competitive advantage of British Sugar as a company. [8]

Case Study 2

The construction of a biomass CHP plant at Grainger Sawmills, Enniskeane, Co. Cork in 2003 marked the development of the first such installation to be built in Ireland. This project was a joint venture between Grainger Sawmills Limited and SWS Group. The concept was to design and construct an operational plant generating green energy (Heat and electricity) from wood by-products such as sawdust, bark, peelings and forest thinnings.

There was a plentiful supply of the raw material on site at Grainger's saw mill with more than sufficient quantites of sawdust and bark being produced in the sawmill and they also has good contacts in the forestry world from buying the timber from foresters to be able to secure supply of forestry thinning.

The project cost €6.2 mm and has a capacity of Electrical output 1.8MWe and Thermal output 7.88MWth. This is enough green electricity to power 3000 houses. This energy is sold back into the national grid,

CHP PERFORMANCE VALUES for Grainger Sawmills

PERFORMANCE VALUES:

Boiler Efficiency 88%

Electrical Efficiency 21.13%

Average Electrical Output 2175 kWe/hr

EMISSIONS VALUES:

Measured Values Licence Values

Dust 12mg/Nm3

50mg/Nm3

Co 92mg/Nm3

200mg/Nm3

NO2

214mg/Nm3

500mg/Nm3

PLANT AVAILABILITY:

Steam Availability 99%

Electrical Generation 97% [9]

CHP plants have to potential to greatly add to industrial steam production in Ireland. Even in the form of fossil fuel burning plants they can reduce the company's carbon emissions and increase their energy cost expenditure due to electricity production.

Conclusion

There is much room for improvement in Ireland to reduce our carbon footprint in relation to steam generation.

• more extensive use CHP plans could make more efficient use of the steam and would have the potential to produce green electricity

• use of biomass boilers on an industrial setting is mixed bag

  • reduced carbon footprint

  • potentially expensive modifications to boilers for biomass burning

  • timber pellets cheaper to buy- currently

    • as of today 1 st December 2001 one tonne of timber pellets(calorific equivalent of 400 litres of heating oil) costs €346, one bag of coal €18.50, bale of peat briquettes €3.99- information from SEAI and Ukwoodpellets.eu

• all lot of the technologies are still in trials or only in early commercial plants in Europe, even so Ireland is still behind Europe in power/steam generated from renewable

• there are issues in Ireland relating to security of supply of biomass feedstocks.

1. http://www.agriculture.gov.ie/agri-foodindustry/foodharvest2020/

2.http://www.spiraxsarco.com/resources/steam-engineering-tutorials/the-boiler-house/shell-boilers.asp

3. http://www.ieabioenergytask32.com/

4. http://www.ieabioenergy.com/LibItem.aspx?id=6780

5. http://www.erec.org/fileadmin/erec_docs/Projcet_Documents/RESTMAC/Brochure4_Cogeneration_low_res.pdf

6. http://www.chpa.co.uk/advantages--benefits-of-chp_183.html

7. http://www.unendlich-viel-energie.de/en/electricity/details/browse/1/article/111/functioning-principles-of-a-biomass-combined-heat-and-power-chp-station.html

8. http://www.britishsugar.co.uk/Electricity.aspx

9. http://www.seai.ie/Renewables/Bioenergy/Wood_Energy/Technologies/Commercial/Graingers,_Ireland's_first_biomass_CHP_plant.pdf

10. http://www.ensyn.com/wp-content/uploads/2011/07/HoustonResidConferenceEnsynPPT2011.pdf