Second volume Seventh issue April 2005 i Bioenergy research

From straw to gas 1 From straw to gas Danish Fluid Bed Technology is Since 1999, the development of the far ahead with the development technology has been supported by a of a new technology in order to grant of DKK 10 million from the Dan- Standards for biofuels 3 ish Energy Authority, and the part of transform the more difficult the PSO programme administered by types of biomass into combusti- Eltra. Apart from Danish Fluid Bed ble gas. This makes it possible to Technology, researchers from the Tech- Biomass-fired choose between several differ- nical University of , as well as CHP plants 4 ent types of fuel and also to re- Danish energy companies Elsam, Force duce the maintenance costs at and Rica Tec, have taken part in devel- oping this new technology. the major power plants. The gasification plant is based on a Six million cubic metres so-called circulating fluid bed, which By Torben Skøtt works at relatively low temperatures of of biogas are lost 6 around 700°C. There are two chambers Gasification is not a new invention, but in the plant: In the first chamber, the not until recently have researchers straw is heated up to 650°C; As there is found out how to treat the more unman- no oxygen inside, the straw does not Criticism of new biogas ageable fuels such as straw and live- burst into flames, but is instead trans- knowledge centre 7 stock manure. formed into 80 percent gas and 20 per- It is the company Danish Fluid Bed cent ash-containing particles of coke. In Technology which spearheads the de- the next chamber, the coke particles are velopment of the technology. For a transformed to gas, leaving a small From straw to ethanol 8 number of years, they have moved from amount of ash, which may partly be re- laboratory scale to a 50 kW test plant used as fertilizer. Both chambers con- and on to a 500 kW plant, which was tain sand that circulates between them, recently tested very successfully at the which thus helps secure a stable tem- Technical University of Denmark. perature level. u Gasification

"The tests were carried out using bales of straw from Kolindsund on Djursland. Here, the soil contains a lot of salt and consequently, a high con- tent of alkaline salts, including chlo- rine, which will normally make a boiler plant corrode within a short period of time. Furthermore, the straw from Kolindsund has an ash content of 12 percent, whereas straw from other parts of the country normally contain only 4-5 percent ash." "We have consciously chosen the worst possible fuel. Power plants can- not analyse every load of fuel they re- ceive, so they must be sure the plant will function using a wide range of dif-

photo: danish fluid bed technology ferent fuels," explains Peder Stoholm. photo: danish fluid bed technology The gasification plant during prepara- At the smaller 50 kW plant, they have The gasification plant during testing at tions at the Technical University of successfully degassed both straw, wood, the Technical University of Denmark. Denmark. chicken manure and pig manure. How- ever, wood has only been the subject for u The gasification plant produces a one trial, as it may be utilized more easily burn it in a boiler, instead of burning hot, tarry gas, which is suitable for in many other energy plants. the fuel directly in the boiler. large power plant boilers, where coat- But there is a purpose to all this. ing and corrosion often pose problems Many advantages Firstly, you avoid problems with slag- when the biomass is combusted di- At first, it may seem troublesome to ging, corrosion and ruined environ- rectly in the boiler. The gas, however, first transform the fuel to gas and then ment plants, which cost the power cannot directly be used for engine fuel because of the high tar contents. The so-called two-step gasifier, which we How the gasifier works mentioned in the latest issue of Bioenergy Research, is more suitable Primary Secondary Pulverized fuel is added to the bottom cyclone cyclone for this job. Gas of the pyrolysis chamber, where it is If the gasifier is to be used for en- heated up to 650°C. As there is no gines, it is necessary to remove the oxygen inside, the straw does not high tar contents from the gas. This is burst into flames, but is transformed not a simple process, but it is techni- into 80 percent pyrolysis gas and 20 Pyrolysis gas percent coke. A stream of circulating cally possible. In small engines, the Coke residue two-step gasifier will probably be more sand particles takes the coke parti- suitable, whereas for engines of several cles with it, after which they are sepa- MW, the fluid bed gasifier will be the rated by a primary cyclone and re- more obvious choice, as it is easier to circulated to the bottom of the pyroly- increase in scale. sis chamber through a reactor, which transforms coke to gas. Ash The worst straw in the world By gasifying the coke in a separate For the past few months, researchers chamber it is possible to keep pro- have carried out two tests using straw cess temperatures low, so the ash in the 500 kW plant and at the mo- does not melt. The ash, including al- ment, they are planning to carry out a kaline salts and phosphor, can then series of tests using livestock manure be separated, resulting in a gas which as fuel. does not cause slagging and corro- Fuel sion. The nutritious ash may then be "We chose the worst straw in the 650 °C 730 °C world for the two tests, and it still went Air reused as fertilizer and probably also well," says Peder Stoholm, managing as a source of potassium and phos- director of Danish Fluid Bed Tech- phor in the production of fertilizer. nology. Pyrolysis Fluid bed

2 Bioenergy research no. 7 • April 2005 Gasification

plants a lot of money every year. Sec- ondly, you can utilize different and thus also cheaper fuels, such as grain residue and sewage. Thirdly, the gasifi- cation technology will make it easier to reuse the ash from the power plants, in- stead of burning coal and straw in the same boiler as it is done today. According to Peder Stoholm, the gasification plant may also be a cheap alternative to the many biogas plants, because nearly the entire process takes place within a few seconds instead of weeks. He imagines that the manure is separated at the farms, after which the solid fraction is transported to a com- munal gasification plant. The transport costs will be limited, as only the solid photo: danish fluid bed technology fraction will be transported, and it will The 50 kW plant at the Technical University of Denmark. At this plant, tests on the be possible to reuse the contents of gasification of wood chips, straw, pig manure and chicken manure have been per- phosphor and potash of the manure, formed. which are concentrated in the ash. However, biological gasification are to be reduced or removed alto- considerable export of both know- also offers a number of advantages, so gether. how and plants. Many of the world's another possibility is to only gasify the resources of biomass are difficult to phosphor-containing fibre residue from Great export opportunities utilize, especially for the production of the biogas plants. Following the successful tests, re- electricity. This is the case with rice Existing legislation does not allow searchers have now started planning an straw and cotton waste; and the increas- the burning of livestock manure. Re- upgrade to 5-10 MW. The gasifier is to ing problems with livestock manure and cently, however, an interdepartmental be upgraded to a size of 100 MW, al- sewage are definitely not just a Danish committee has been set up, which, by 1 lowing it to supply gas for an entire phenomenon. In many cases, the fuels June, must present a draft on whether power plant block. simply lie and rot, and are thus contrib- this legislation is to be changed, in- Peder Stoholm predicts that the tech- uting to the greenhouse effect as well cluding whether the duties on burning nology may open up the possibility of a polluting the water environment. n

BioNorm concluded Liquid biofuels Solid biofuels The EU-financed research project In December 2002, the European Com- The Danish standardization commit- BioNorm has now been concluded. mittee for Standardization, CEN, ap- tee for solid biofuels has been very Originally, it was the idea that the pointed a task group, BT/WG 149, to active within the European work BioNorm results were to be used in introduce the need for standardization on standardization, and has influ- connection with upgrading the technical of alternative liquids and gaseous fuels. enced many exisisting and future standards to European standards after The task group has just published a standards. three years. Already today, many of the report which concludes that there is a The European task group for the results are being used in the technical need for standardization in this field. standardization of solid biofuels, standards which have just been pub- This applies to fuels for motorized CEN/TC 335, has a total of 30 subject lished, or will be soon. vehicles as well as stationary plants. matters. The first standards have now However, there are still quite a few Denmark is one of the few countries been published. Among these are stan- loose ends. There are areas which require in the EU that does not use liquid dards concerning definitions of solid further research and there are areas which biofuels as engine fuel. Limited biofuels, as well as standards for defin- have not been discussed in BioNorm. amounts of biodiesel are used for ing water and ash contents. Therefore, an application for a new pro- heating, though. ject, BioNorm II, has been submitted. Source: Dansk Standard, no. 1-2005. Source: Dansk Standard, no. 1-2005. For further information, please contact Source: Dansk Standard, no. 1-2005. For further information, please contact Charlotte Vincent Fischer, [email protected] For further information, please contact Charlotte Vincent Fischer, [email protected] Charlotte Vincent Fischer, [email protected]

Bioenergy research no. 7 • April 2005 3 CHP plants

Biomass-fired CHP plants

- in theory and in practice photo: torben skøtt/biopress Researchers still have problems The CHP plant on Masnedø has far fewer slagging problems than the plant in explaining the various opera- -Sakskøbing, even though the two plants are practically identical. tional problems at biomass-fired promote the continued technical devel- can be seen in figure 1, which shows CHP plants. A better under- opment in the field by focusing and the amount of biomass used at Danish standing of the physical and qualifying future research and develop- power plants. chemical conditions in a bio- ment efforts. The oldest straw-fired plant is mass-fired power plant boiler is As part of these efforts, Elsam and CHP plant, established in 1989. needed, as is an improved ex- ENERGI E2 held a seminar on bio- It is a so-called cigar-fired plant, where change of know-how between mass combustion on 14 March. The combustion takes place directly at the objective of the seminar was to pro- end of straw bales. The plant has an power plants in the eastern and mote dialogue between the production electrical output capacity of 5.0 MW western parts of Denmark. staff and the technical development and burns approx. 25,000 tonnes of staff working at the head offices. straw per year. The seminar was a mixture of lec- At the other end of the scale is the tures and discussions. The lectures de- boiler fired by wood pellets at the By Torben Kvist Jensen scribed E2's operational experiences Avedøre plant. The wood pellets are from decentralized biomass plants and not fed directly into the boiler, but are Since the end of the 1980s, Danish en- the Avedøre plant, as well as Elsam's ground in three wooden mills and then ergy companies Elsam and ENERGI experiences with the straw boiler at the blown into the boiler as roughly 2 mm E2 have been building and running Ensted plant and adding straw to coal particles. The plant produces up to 560 CHP plants based on biomass combus- at the Studstrup plant. Furthermore, MW of electricity, and is able to burn tion, and currently, large amounts of speeches from the Technical Univer- approx. 300,000 tonnes of wood pellets biomass are introduced to central sity of Denmark on research in boiler per year. Apart from wood pellets, they plants. During the whole course the slagging and corrosion conditions were also burn around 150,000 tonnes of technology has been developed and re- given. Finally, University pre- straw in a separate grate-fired boiler at search and development projects have sented their work with modelling in the Avedøre plant. With the latest bio- taken place. Together with Danish en- connection with biomass combustion. mass-fired plants at the Studstrup plant ergy company Elkraft System, the two and the Amager plant, an installed ca- companies have started a project to 1.4 million tonnes of biomass pacity with the equivalent of around gather the development activities that The rapid development of biomass fuel 1.5 million tonnes of biomass functions have already been carried out, and to combustion over the past many years at Danish CHP plants today.

4 Bioenergy research no. 7 • April 2005 CHP plants

The biggest problems with the bio- The straw-fired CHP plant in mass-fired plants stem from handling has a substantially higher CO emission and pre-processing the fuel. This is the than the other straw-fired plants. case with both the small grate-fired plants and the large suspension-fired plants, in which the fuel is burnt while floating up through the boiler. need to better understand the physical Operational problems and chemical conditions. As a measure of what poses opera- Apart from the concrete examples tional problems, the number of call-ins from E2's straw-fired plants, a number to decentralized biomass-fired plants of other subjects were mentioned, manned during the daytime only was which require extra research and devel- used. These statistics show that prob- opment efforts. As an example, we can lems with straw transports and the photo: torben skøtt/biopress mention the use of additives for slag- combustion plant are generally the rea- as the plant has considerably fewer ging reduction and the reutilization of sons why the staff has to work outside slagging problems when firing with biomass ash. standard hours. In addition, problems straw than at the plant in Maribo- Another result of the seminar was with heat surface slagging as well as Sakskøbing. that both Elsam's and E2's operational wear and tear were mentioned. staff became aware of the fact that they By comparing operational data from Need for better models have the same problems on both sides various plants, it turns out that there Several projects have developed mod- of the Danish Great Belt, and that there are great differences in the CO emis- els for describing the combustion of may help at hand from each other. sion from E2's straw-fired plants. biomass in grate-fired plants. If these There was consensus that we must con- Slagelse Kraftvarmeværk, a CHP models were able to explain why the tinue our work, and that we should es- plant, is a grate-fired plant which uses conditions are so different, as the ex- tablish a forum for the exchange of op- a push-grate. This means that the layer amples from Slagelse, Haslev og erational experiences within biomass of straw on the grate is steadily pushed Maribo-Sakskøbing show, we would combustion. down over the grate, as opposed to have a good tool. It would be possible plants with a vibration-grate, where the to reduce emissions and the number of Torben Kvist Jensen is an engineer layer on the grate is vibrated at inter- boiler stoppages because of poor heat- employed in the research and develop- vals causing great peaks in the CO ing intake. But before we can describe ment department of ENERGI E2. emission. these conditions by using models, we E-mail: [email protected]. n One would therefore expect the CO emission for the plant in Slagelse to be Millions of tonnes of biomass/year low, but this is not the case. The CO 1,6 emission is actually considerably 1,4 higher than for E2's other straw-fired plants. 1,2 At Haslev Kraftvarmeværk, another CHP plant, the NOx emission was ex- 1,0 pected to be high because of the highly 0,8 concentrated combustion, a result of the cigar-fuelling principle. However, 0,6 operational data show that the NOx emission from Haslev does not differ 0,4 greatly from other small de-centralized 0,2 plants. At Maribo-Sakskøbing there have 0 been problems with boiler wall slag- 5 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 200 ging, which has not been registered at Masnedø, despite the similarity of the Køge (blok 7) Grenå Køge (blok 8) Studstrup two boilers. There are few differences Haslev Måbjerg Maribo/Sakskøbing Amager in the version of the boiler, and at Rudkøbing Masnedø Avedøre Masnedø they sometimes fire up to 25 Slagelse Ensted percent wood chips. Apparently, the Figure 1: Installed capacity for biomass combustion at Danish CHP plants. wood chips do not make a difference,

Bioenergy research no. 7 • April 2005 5 Biogas

The vast majority of common biogas plants has established gas reception from the so-called after-storage tanks. The picture shows the biogas plant at Vaarst-Fjellerad in Northern Jutland, where a third of the gas production co- mes from the covered storage tanks. photo: torben skøtt/biopress Six million cubic metres of biogas are lost

Every year, six million cubic tor capacity. Many common plants three million cubic metres of methane metres of methane gas are lost only have the capacity for a retention per year, which equals an annual in Danish common biogas facili- time of a few weeks, or much less than income of around DKK 10 million. the two months it would take for the ties. This equals the production full gas potential to be exploited. Reasons of almost three large common However, many plants will undoubt- There may be many reasons why the plants with a 100,000-tonne bio- edly be able to improve their financial gas potential is not exploited suffi- mass capacity per year. status by focusing on the residual po- ciently. First and foremost is the ques- tential. The study conducted by the tion of how long the biomass retention Technical University of Denmark com- time is in the plant. A short retention By Torben Skøtt prises 18 plants. Imagine the poorest time will entail a low gas production half of these plants improving to the per cubic metre of biomass, and if the There is a great difference between average of the best one-third; then the retention time is shorter than 15 days, a how much gas Danish common biogas average loss per cubic metre biomass considerable reactor loss will ensue. facilities are able to extract from live- would be halved. This could result in In order to extend the retention time, stock manure and organic waste. This an additional production of around and thus increase the gas yield, most is the result of a study at the Environ- common plants have established gas ment & Resources department at the Further information reception from the storage tanks Technical University of Denmark. (so-called after-storage tanks). How- On average, around 87 percent of The report "Kortlægning og doku- ever, a few plants still do not exploit the gas potential are exploited for en- mentation af procesforhold på dan- the gas production from the storage ergy production at the common plants, ske biogasanlæg" (Mapping and tanks, which of course entails a consid- but there are plants capable of exploit- documentation of process conditions erable loss of methane. ing almost 98 percent of the potential, at Danish biogas plants) is prepared Experience shows that the gas pro- whilst others exploit only 73 percent. by the Environment & Resources duction from the after-storage tanks is For every cubic metre of biomass department at the Technical Univer- highly dependent on temperature. Af- treated at the plants, about 4.2 cubic sity of Denmark. ter-rotting from thermophilous plants metres of methane are not being ex- Rena Angelidaki was responsible should take place at no less than 30°C. ploited. This amounts to six million cu- for the project, whilst Majbrit Stavn Mesophilous plant temperatures should bic metres per year, equal to the pro- Jensen has been the overall resource be at least 25°C. Gasification more or duction at three large common plants person on the project. Anette Hejn- less stops when the temperature drops with a capacity of 100,000 tonnes of felt was the editor of the report. below 15°C, but as soon as it increases, biomass per year. Several students have participated in the methane production is activated From a financial point of view, sub- the project as well. immediately. stantial losses are involved. In practice, It is not only the retention time that however, exploiting the entire residual The report may be downloaded from influences the gas yield. The plants potential is unrealistic, as it would re- BiogasForum Öresund's homepage: which lose the most methane generally quire a considerable expansion of reac- www.biogasforum.dk. have a lower biomass manure content,

6 Bioenergy research no. 7 • April 2005 Biogas

and thus larger contents of organic Cubic metre of methane/cubic metre of biomass waste. Generally, they also have a 12 higher VFA level, indicating that the 10 biological process becomes unstable more easily. Finally, mesophilous 8 plants generally lose more methane 6 than thermophilous plants. 4 Methane leakage from manure storages 2 One would fear that a poor utilization 0 of methane gas in biogas plants would NystedHashøj Lintrup ThorsøBlåhøjVeggerFangel Filskov lead to a considerable leakage of meth- Sinding Blåbjerg Snertinge Revninge ane from the subsequent manure Studsgård Århus (mesofil) Vaarst-Fjellerad Århus (termofil) storages. A greater leakage of methane Vester Hjermitslev from storing the partly degassed bio- Lost methane gas compared with the amount of biomass processed by the mass than from raw manure would thus plants. This loss has been calculated after the final step of the process, i.e. after partly counteract the CO2 advantages the biomass has been through both reactors and after-storage tanks. For the which the biogas plant entails. plant in Århus, the loss has been calculated individually for the mesophilous However, not much indicates that and the thermophilous lines. this is the case. As mentioned before, the development of methane nearly stops when the temperature is below ing partly degassed biomass makes up than the methane development from 15°C, and as the average temperature a maximum of 10 percent of the resid- raw manure, as they need data con- in Denmark is only 8°C, the develop- ual potential, or approximately 1.2 per- cerning methane development from ment of methane in the storage tanks is cent of the potential in raw manure. raw manure. In practice, the leakage highly limited. The study from the Technical Univer- from raw manure may actually prove Researchers have calculated that the sity of Denmark does not give a final higher because of the larger gas po- methane development gained by stor- answer of whether that is more or less tential. n

Criticism of new biogas knowledge centre

The Association of Danish Biogas ment projects, something that contrib- Plants severely criticizes the new uted greatly to the development." centre for livestock manure and "This possibility no longer exists. manure technology in Foulum. Instead, they have chosen to spend This surfaced at the annual gen- DKK 150 million on a single centre, eral meeting on 26 February in and it hurts that they do not value our Bøstrup near Slagelse. experiences higher," stated Aksel Buchholt at the annual general meeting The association is very satisfied that of the biogas association on 26 more funds are being made available February. for research in biogas and manure He was of the opinion that the cen- separation, but is also highly critical tre had been placed in Foulum because of the model chosen by the govern- the research facility needed a biogas ment. In the future, the vast majority plant to solve the problems with excess of the funds is to be spent on a newly manure. established centre at the Danish Insti- "In January, the centre was pre- tute of Agricultural Sciences in photo: torben skøtt/biopress sented at a large seminar at the Univer- Foulum - a detrimental development, Chairman of Danske Biogasanlæg sity of Southern Denmark in , according to Aksel Buchholt, chair- (Danish Biogas Plants) Aksel Buchholt but no debate ensued. There were no man of the Association of Danish at the annual general meeting of the opportunities to ask questions, and it Biogas Plants) . association on 26 February. was all purely one-way communica- "It is a shame that they do not fully tion," stated Aksel Buchholt, who re- utilize the experiences gathered at the country. Previously, we could apply quested far greater openness on the many common plants throughout the for grants to finance concrete develop- part of the centre. TS

Bioenergy research no. 7 • April 2005 7 FiB – Bioenergy Research is pub- lished with support from Denmark’s From straw to ethanol Energy Research Programme, Elsam and Energi E2. The newsletter, which is free of charge, is published six times a year both in a Danish and an English version. Both versions can be downloaded from the Internet at the following homepage: www.biopress.dk

The Danish version of the newsletter is also available in a printed version supplied as an insert in the Danish magazine, Dansk BioEnergi. Further copies of the Danish version can be ordered from BioPress, via the fol- photo: torben skøtt/biopress lowing e-mail address: Danish energy company Elsam rectors to be able to make a decision in [email protected], or telephone now goes a step further with its mid-May on whether the company number +45 86 17 34 07. big ethanol project, IBUS. Before should establish a traditional ethanol the summer holidays, a new pilot production. Editor responsible: Torben Skøtt plant capable of handling one At the same time, technicians are in tonne of straw per hour, is to the process of establishing a pilot plant Production: be ready at Danish power plant at Fynsværket, which should be able to BioPress Fynsværket, and in the middle convert one tonne of straw per hour Vestre Skovvej 8 of May, the board at Elsam must into ethanol, fuel or animal feed. The DK-8240 Risskov decide whether to establish an plant, which is a part of the ambitious Telephone +45 8617 3407 ethanol factory based on known IBUS project and has been in operation Telefax +45 8617 8507 technology. since the summer of 2003, is the fur- E-mail: [email protected] ther development of a small test plant Homepage: www.biopress.dk Elsam are still working determinedly to to process 100 kilos of straw per hour. be able to convert straw and waste to The pre-treatment of straw has been Photo on the front page: ethanol, but now they are also consid- the primary job at the test plant . The Danish Fluid Bed Technology ering starting a more traditional produc- new plant will especially be used for and BioPress tion of ethanol, based on sugar beets or research in the ethanol process itself, grain. This was stated by Elsam re- including tests of the bacteria and en- Copies printed: 4,000 search manager Charles Nielsen at a zymes necessary for converting raw meeting at Fynsværket on 5 April. The materials containing cellulose into Print: CS Grafisk. The magazine has meeting had been arranged by the plant liquid ethanol. been printed on environment-friendly in cooperation with the Danish Know- By combining ethanol production offset paper. ledge Centre for Livestock Manure and with the production at a power plant, Biomass Technology. the costs can be reduced significantly. Reproduction of articles or illustra- Charles Nielsen is convinced that Therefore, Elsam calculates that with tions has to be accepted by BioPress. the transport sector energy consump- a traditional ethanol production, the It is allowed to quote articles if the tion will be based increasingly on etha- costs may be reduced by around 20 source is clearly indicated. nol, but he also estimates that for the percent. This will reduce the price of a first many years, the more traditional litre of ethanol to around DKK 2.50, or Next issue: ethanol production will dominate the approx. DKK 0.80 below the European to be published in the middle of market. Therefore, Danish energy com- market price. This will give Elsam a June 2005. The deadline for articles pany Elsam have begun to sort out in- clear competitive advantage compared is 16 May 2005. formation in order for the board of di- to other producers on the market. TS