PowerGen Europe 2003 Conference, Düsseldorf, Germany, 6 – 8 May, 2003 1(18) Mr. Kari Niemelä Foster Wheeler Energie GmbH, Burggrafenstraße 5a, D 40545 Düsseldorf, Germany Mr. Kim Westerlund Foster Wheeler Energie GmbH, Burggrafenstraße 5a, D 40545 Düsseldorf, Germany Experience of fluidised bed technology for biomass plants in different applications and development towards new applications in RDF burning. 0. Abstract The biomass boilers in fluidised bed technology have gone over a remarkable development dur- ing the past twenty years starting from the bark boilers and ending to the demolition wood boil- ers. The boilers have been developed further according to the demands for RDF and municipal solid waste burning. The changes in the boiler plant have been partly mechanical changes and changes brought by the material technology but also with the more demanding fuels changes in the boiler process and boiler parameters. The basis of the biomass boilers is in the pulp und paper industry and typically from the bark and sludge fired power boilers. In the eighties and also nineties the pulp mill internal wastes, bark and waste water sludge were typically burned in bubbling fluidised boilers or later also in circulating fluidised bed boilers and process steam was generated with this waste material. The fuels were relatively easy to burn with fluidised bed technology compared with previous grate boilers. During the years the requirements in emissions have been tightened all over the Europe, and this has caused changes in the fluid bed processes burning different bio fuels The governmental supports for generating electricity with biomass has caused especially in Central Europe that the interest of burning biomasses like demolition wood has become re- markably higher. Demolition wood is the only possible fuel in Central Europe to give the interest- ing volume needed. These fuels have again caused changes both in mechanical parts and in the process of the boilers not to forget the material technology. At the same time new require- ments have been placed for the emissions of the plants and they form partly the design parame- ters of the new plants. Because of the shortage of the fuel and the high price of the electricity there has been also an increasing interest to invest for higher efficiencies and higher availabilities of the plants. The technological development in fluid bed technology has made it possible to offer these features for the plants. After the biomass the RDF burning will be the next step also for fluid bed technology. This de- velopment is accelerated now by the new directives. The modifications are already made and the technology is proven. Numerous plats for RDF and possibly for sludge will be built during the coming years. Modified fluid bed technologies like gasifying will be probably part of this de- velopment. Fluid bed technology will have the future also with different biomass and waste ma- terials by modifying actively the technology and applications and developing necessary systems for monitoring and supporting the operation.
Transcript
PowerGen Europe 2003 Conference, Düsseldorf, Germany, 6 – 8 May, 2003
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Mr. Kari Niemelä Foster Wheeler Energie GmbH, Burggrafenstraße 5a, D 40545 Düsseldorf, Germany
Mr. Kim Westerlund
Foster Wheeler Energie GmbH, Burggrafenstraße 5a, D 40545 Düsseldorf, Germany Experience of fluidised bed technology for biomass plants in different applications and development towards new applications in RDF burning. 0. Abstract The biomass boilers in fluidised bed technology have gone over a remarkable development dur-ing the past twenty years starting from the bark boilers and ending to the demolition wood boil-ers. The boilers have been developed further according to the demands for RDF and municipal solid waste burning. The changes in the boiler plant have been partly mechanical changes and changes brought by the material technology but also with the more demanding fuels changes in the boiler process and boiler parameters. The basis of the biomass boilers is in the pulp und paper industry and typically from the bark and sludge fired power boilers. In the eighties and also nineties the pulp mill internal wastes, bark and waste water sludge were typically burned in bubbling fluidised boilers or later also in circulating fluidised bed boilers and process steam was generated with this waste material. The fuels were relatively easy to burn with fluidised bed technology compared with previous grate boilers. During the years the requirements in emissions have been tightened all over the Europe, and this has caused changes in the fluid bed processes burning different bio fuels The governmental supports for generating electricity with biomass has caused especially in Central Europe that the interest of burning biomasses like demolition wood has become re-markably higher. Demolition wood is the only possible fuel in Central Europe to give the interest-ing volume needed. These fuels have again caused changes both in mechanical parts and in the process of the boilers not to forget the material technology. At the same time new require-ments have been placed for the emissions of the plants and they form partly the design parame-ters of the new plants. Because of the shortage of the fuel and the high price of the electricity there has been also an increasing interest to invest for higher efficiencies and higher availabilities of the plants. The technological development in fluid bed technology has made it possible to offer these features for the plants. After the biomass the RDF burning will be the next step also for fluid bed technology. This de-velopment is accelerated now by the new directives. The modifications are already made and the technology is proven. Numerous plats for RDF and possibly for sludge will be built during the coming years. Modified fluid bed technologies like gasifying will be probably part of this de-velopment. Fluid bed technology will have the future also with different biomass and waste ma-terials by modifying actively the technology and applications and developing necessary systems for monitoring and supporting the operation.
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CONTENTS 0. Abstract 1. Introduction 2. Bubbling fluidised bed technology for biomass (BFB) 3. Circulating fluidised bed technology for biomass (CFB) 4. Second generation of CFB boilers for biomass 5. Third generation CFB plants for demolition wood and with INTREC TM concept
6. The CFB technology with INTREC TM superheaterin W-T-E concept for RDF type of fuels
7. Current market situation and trends for the future
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1. Introduction The fluid bed technology have started with biomass combustion in pulp and paper industry. The boilers have the basis from the bark burning from that time. Fluid bed technology replaced e.g. grate fired technology in Scandinavia already almost totally during the eighties. Different type of biomasses have been introduced to the market and the fuels have been burned with bubbling fluid bed (BFB) and circulating fluid bed (CFB) technologies. With new fuels and new require-ments modifications were needed for the technology and it is possible to differentiate several generations in the technology. There has always been a desire to burn some waste materials in the bio mass plants, but the plants were designed as bio mass power plants. The trend seems to be now towards different wastes like RDF and sludge. The boilers for these fuels will also be based on the earlier technology but will already be designed for the remarkably higher de-mands. A RDF based power plant with differs already remarkably from a high availability bio-mass power plant with high efficiency. In this paper we shall mainly inform of the development of the fluid bed technology in biomass burning first in Scandinavia and then later on also from Central Europe. We describe different fluid bed applications, which have the basis anyhow in the bark boilers from the eighties. The examples are taken mainly from the market in Scandinavia, which is the leading market for bio-mass plants and from Germany because of our daily operation on that market.
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2. Bubbling Fluidised Bed technology for biomass (BFB) During the end of seventies and eighties the biomass firing was mainly common in the power plants in pulp and paper industry where bark, other wood wastes and sludge from the process were burned with fluid bed technology. Both bubbling fluid bed and slightly later circulating fluid bed were used. Often several fuels were used simultaneously and no special care was given that the plants were specially biomass plants. The target was to dispose the waste materials bark from the wood yard and the waste water sludge from the plant and to generate at the same time some process steam. The plants had normally energy enough through the recovery boiler. The driving force for the investments was the waste disposal. The fuels, normally bark and sludge, were not very easy to burn with conventional methods like with grate boilers. Fluidised bed offered a good opportunity to burn simultaneously these high moisture content fuels. These fuels were not especially difficult to burn in bubbling fluid beds or circulating fluid beds. The emission requirements were not either at that time very strict and these limits were possible to meet with fluid bed burning without extra methods. During the eighties and nineties bubbling fluid bed boilers replaced nearly totally the grate fired boilers in Scandinavia especially in biomass firing. There were at that time several suppliers of fluid bed technology in Scandinavia. These boilers were the basis for future bubbling bed biomass boilers. After this there has been different mechanical and also process changes in the plants in order to meet the requirements of the market.
Picture: Forssa bubbling bed boiler 57 MWt
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As examples of BFB boilers built by FW at that time were in pulp and paper industry: Stracel, Strasbourg 39 MWt 480 °C/88 bar bark/sludge 1990 Golbey 45 MWt Sat./25 bar bark/sludge 1991 Rauma 60 MWt 465 °C/62 bar bark/sludge 1990 Metsä.Botnia Kemi 115 MWt 480°C/85 bar bark/sludge 1994 the last one a typical boiler conversion from a grate fired boiler and examples from municipalities: Falun 30 MWt 510°C/63 bar bark/chips 1993 Kristianstad 50 MWt 513°C/68 bar forest resid. 1994 Kankaanpää 24 MWt 510°C/60 bar bark/chips 1992 Ylivieska 24 MWt 510°C/61 bar bark/chips 1994 Forssa 57 MWt 510°C/61 bar bark/chips 1996 In the Forssa plant already also test combustion of RDF type fuel was carried out in the nineties. Availabilities were not measured and corrosion and fouling were normally a problem only when some new and unknown fuels were burned, like waste materials. Bubbling bed technology remained mainly in Scandinavia as a technology for the smaller boilers and especially in Finland a technology for the pulp and paper industry. During and after the nineties several bubbling bed biomass plants with similar technology as described above have still been built in Scandinavia, but also several larger bubbling bed boil-ers for the pulp mills. These bubbling beds have typically bark other wood residues and sludge as fuels. The plants typically have rather high steam parameters for higher efficiency and the availability of the plants is secured with the design and lay-out of the heat surfaces and with material technology using the remarkably better materials in the super heaters than earlier. As Examples of the pulp mill plants: Anjalankoski 88 MWt 525°C/115 bar bark, sludge 2001 wood resid. Jämsänkoski 185 MWt 535°C/107 bar bark, sludge 2002 wood resid. Äänekoski 157 MWt 535°C/105 bar bark, sludge 2002 (picture) wood resid. During the past decades the bubbling fluid bed boiler concept has not changed very much. The fuels are very much the same as earlier. The emission requirements have changed the process somewhat and also the requirements for availability. The design and materials used for the su-perheaters with the high steam parameters ensure anyhow a good availability for these boilers.
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Picture: Äänekoski-Äänenvoima EPC power plant with 157 MWt BFB boiler 3. Circulating fluidised bed technology for biomass (CFB) During the eighties the development of circulating fluidised bed technology was especially strong with fossil fuels. One reason was the SO2 emission and the capture of sulphur already in the fluid bed boiler furnace and the avoiding a separate sulphur removal in the plant. CFB was anyhow also introduced for the same purpose as bubbling beds during the same time. One reason was that the process industry and the municipal power plants wanted to have the opportunity to introduce also coal or other fossil fuels as an alternative fuel for the plants. Almost all of the plants are designed and calculated also for simultaneous burning of coal although the main fuels were possibly bark, other wood residues and water treatment sludge. The fuels were also relatively easy to burn with CFB`s. With some sludge’s the CFB process had slight fouling problems and in this matter BFB had certain advantages in comparison to CFB boilers. The first commercial CFB were built during the eighties and as examples of these plants: Lenzing in Austria, Östersund in Sweden, and e.g. Perlen, Utzensdorf in Central Europe. Most of the plants were relatively small and actually too small as CFB plants. The 16.3 MWt Uzensdorf plant (470 °C, 60 bar, 16.3 kg/s) in the picture burning bark sludge and paper waste. The plant was commissioned in Uzensdorf paper mil in Switzerland in 1992.
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Emission requirements were still rather low and the CFB:s were chosen mainly because of the fuel flexibility. The parameters in the industrial applications and sludge burning were typically: 450-480 °C/ 60-70 bar. As a typical example the Uzensdorf traditional CFB boiler with a separate uncooled cy-clone as a first generation CFB and typically also with an evaporation bundle and two drum concept. The driving force for these plants was as for the bubbling beds also the disposal of the waste materials, bark and sludge but also to have more fuel flexibility with fossil fuel like coal or brown coal as alternative fuels. The fuels were easy to burn and the impurities of the fuels were relatively low so that e.g. the risk of high temperature corrosion or fouling were not very high. The experience of the plants were generally good. The technology was partly so young that there were still some difficulties in the execution of the circulating fluid bed technology eg. erosion in some parts but a lso fouling was a problem in some boilers. When entering to the bigger plants more CFB plants were built. One reason for this was that the emission requirements in different countries became more importance in the investment. In the beginning of nineties especially in Sweden the government started to support the energy made by bio fuels. With this came also into publicity the expression biomass boiler or biomass power plant. Same type of governmental supports was introduced also in some other countries in Europe. With the same the authorities tightened the emission requirements as a condition of the gov-ernmental support. Sweden was an example of the development of biomass, because Sweden did not want politically to build more nuclear power and rather no t either any other power based on fossil fuels. Several plants were built both with bubbling fluid bed technology and also with circulating fluid bed technology. At this moment the last grate fired boilers were built in Scandinavia for bio-mass. The fuel was untreated wood, but not any more only bark but also wood chips and saw dust and forest residues. The fuel is so different from the earlier bark that concept changes were needed in the boiler process. Especially the ash content and the ash composition were remarkably more difficult to handle also in a fluid bed boiler. Especially the high potassium content of the ash was an important character in the boiler design. The high potassium content caused in the first boil-ers fouling by fastening to the heat surface bundles and on the other hand the high potassium enriched also in the bed, when the used bed material was not enough changed with new make up bed material. The accumulation of potassium in the bed caused light or difficult clinkering of the bed and caused severe unavailability of the plants. One difference also to the old bark boilers was that the overall amount of ash in these fuels was very small, some 1-2 %, and no additional bed material was formed in the bed. Additional make up bed material had to be added in the furnace. In several plants unexpected high amounts of bed material had to be used in order to keep the boiler running properly. These operational diffi-culties were overcome when the operators received more experience of burning this type of wood. It was important to reduce the furnace temperature because of two reasons; first to avoid the agglomeration of the potassium in bed and secondly to lower the NOx emission levels of the boiler. In CFB:s some 850 °C was chosen as a design temperature for the furnace.
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The temperature profile enables some additional applications for a circulating fluid bed com-pared to the bubbling bed while the profile in CFB is almost constant in all areas of circulation. bubbling bed profile has a high temperature area above the fluidised bed. The driving force for these investments were the subvention from the government for new plants and with the same a possibility to build a new power plant for the company fulfilling the tight-ened emission requirements. The reason to choose CFB instead of BFB was normally the fuel flexibility and the possibility of using also fossil fuels if needed in a later phase or as an emergency fuel . It was also easier to meet the emission requirements with a CFB than with a BFB and this was an essential advan-tage of the CFB. This was especially the case with CO and NOx emissions and NOx-emission was bonused remarkably with low levels. Examples of the traditional first generation CFB boiler plants: Stora Enso 150 MWt 535°C/113 bar bark, wood residues 1990 Karlstad 90 MWt 505°C/68 bar forest residues 1992 For the first time a biomass boiler was equipped with DeNOx device. Availability started to be also an important topic the contract negotiations. 4. Second generation of CFB boilers During the first half of nineties Foster Wheeler developed the second generation circulating fluidised bed boiler, where the cyclone was also water cooled and integrated to the other water cooled parts of the boiler. The advantage of this boiler were e.g. the thin refractory in the cy-clone, which fact was at once greeted by the operators because the earlier service need of the thick refractory. The first 5 MWe plant was supplied to Kuhmon Lämpö in Finland burning saw dust and wood chips and after that two peat fired units were supplied to Kokkola (30 MWe) and Rovaniemi (30 MWe) in Finland. The breakthrough with the second generation CFB Compact was done in Sweden in 1994 when three wood waste fired units were sold to the market at the same time; Växjö 100 MWt 540 °C, 142 bar forest residues 1996 Brista 122 MWt 540 °C, 144 bar forest residues 1996 Skellefteå 92 MWt 540 °C, 141 bar forest residues 1996 All three plants are burning forestry residues, saw dust and wood chips. For all investments the driving force was also the high governmental support for the investment, which were again bound for strict emission requirements. It was also then worth investing to the NOx reduction in Sweden because all plants having the values lower than the average were paid a bonus from the other plants over the average. This is why the plants were equipped with ammonia injection although the were burning only wood waste. Växjö plant installed also the catalyser-package in order to remove the ammonia slip and even to lower still somewhat the NOx-emission. The plants were commissioned end of 1996. As an example the picture of the second generation Växjö CFB boiler below
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The emission requirements for Växjö (6 % O2), which limits were easily met in the performance tests. NOx 50 Mg/Nm3 SO2 250 Mg/Nm3 CO 220 Mg/Nm3 Especially the high potassium content and low ash content of the fuel caused some unexpected operational problems in the beginning of the operation in Växjö and Brista boilers. The furnace temperature was deliberately designed somewhat higher than normally in wood fired boilers to avoid the N2O emission, which also was an issue at that time in Sweden. The process changes in these plants were the new boiler concept with cooled cyclone, high steam parameters for wood firing, the ammonia injections and the slip catalyser package for the NOx reduction and additionally the optimised primary/secondary air introduction to the boiler because of low emissions. Although wood has been fired in Scandinavia for decades the burn-ing of e.g. forest residues seemed to be more difficult than expected. The plants had also in ad-dition to strict emission levels also high availability requirements > 95%. Numerous, high steam parameter wood fired boilers of the same type have been since the built especially in Sweden with this technology. 5. Third generation CFB plants for demolition wood with INTREX TM concept The next phase in the Foster Wheeler CFB development was to have an internal heat ex-changer as a final super heater. This development was necessary especially when having impu-rities like chlorine in the fuel. With this development it was possible to avoid fouling and corro-sion of the final super heater. The final super heater was placed in the ash return leg and the super heater bundle is covered and protected then by the ash /bed material. The INTREX TM super heater was built first for one traditional CFB boiler in Denmark burning coal and straw (Grenå), but the first commercial INTREX TM was built in Germany in Hornitex Beeskow plant where demolition wood, production waste and wood dust are burned.
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Hornitex Beeskow plant. The final super heater is placed in the ash return and the super heater is covered and much less in contact with e.g. flue gas with higher chlorine content. The first commercial plant with the INTREX TM concept for demolition wood 20 MWe was built in Hornitex Beeskow chip board plant in Germany in 1996 with parameters 480 °C, 89 bar, 30.5 kg/s. The plant was burning demolition wood in German categories AI-AIV and also production waste from the chip board plant. The boiler is able to burn also very fine dust type of biomass. With this type of waste material it is important that the steam temperature in the super heaters in flue gas flow should according to our opinion not exceed 420-440 °C. The INTREX TM concept gives the possibility of choosing higher steam parameters for the plant and still minimize the risk for fouling and corrosion. In case of Beeskow the steam temperature in convection super heater was about 420 °C and thus the temperature rise in the INTREX TM some 70 degrees. To-day the steam temperature from INTREX TM super heater can be chosen some 20 degrees higher in demolition wood plants in order to improve additionally the efficiency. Today the INTREX TM concept is a standard concept in almost all CFB boilers as final super heater or re-heater. In order to be able to guarantee high availability for the demolition wood plants it is of utmost importance to be able to remove foreign particles, like metals and stones from the grid. An open grid was developed by Foster Wheeler for demolition wood plants and introduced also in Beeskow plant.
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A s c h e A s c h e A s c h e A s c h e
D Ü S E N B O D E N
l e i k k a a / a r i n a . d s 4 / 0 3 9 8 /a m s Pictures: INTREX TM superhestr and an open nozzle step grid for demolition wood The construction of the so called step grid was a very demanding task. Before the grid was re-moving the coarse particles and was not eroded the grid had to be retrofitted three times. At the moment the grid is a standard solution and one important part of ensuring the availability of the plant. Important features for the design of a fluid bed demolition wood plants:
• fuel analysis and particle size • the trace elements of the demolition wood • steam temperature in the flue gas flow • removal of coarse particles from the grid • approval according to 17.BimSchV code
The approval of Beeskow plant was at that time generally 17.BImSchV with some exceptions and the limits were met with very good figures in the plant. Because of the high lead content of Beeskow fuel in the beginning a lead corrosion was noticed in on the heat surfaces in Beeskow. This type of corrosion occurs already in lower temperatures and the origin of the high lead content seemed to be ammunition boxes, which were burned to-gether with the demolition wood. The same final super heater is still in the Beeskow plant. In the following some emission measurements of Beeskow plant (11 % O2): NOx mg/Nm3 < 150 CO mg/Nm3 < 10 HCl mg/Nm3 < 10 HF mg/Nm3 0
INTREX™Überhitzer
Festpartikel-Rückführschacht
Externe Zirkulations-öffnungen
Festpartikel-Rückführkanäle
Lufteintriff
INTREX™Überhitzer
Interne Zirkulations-öffnungen
ger/cfb/intrex.ds4/0499/ams
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The flue gas cleaning is a fabric filter with limestone and active carbon as additives. In some cases a pre separation cyclone is needed before the fabric filter. In the year 2000 Foster Wheeler supplied a similar boiler for Hornitex Horn plant. The fuels and also the parameters were very similar to Beeskow plant. In Horn plant the steam temperature after the second super heater is still lower than in Beeskow, some 400 °C . The fuel in these plants is demolishing wood, all or selected from category A1 to A4. The fuel price is partly connected to the trace element levels in the fuel: The typical fuel for demolition wood plants :
Unit Average Range Lower heating value MJ/kg 14 12 - 17 Moisture % 26 20 - 34 Ash % d.m. 15 9 - 22 Carbon (C) % d.m. 48 Hydrogen (H) % d.m. 6,4 Oxygen (O) % d.m. 29 Nitrogen (N) % d.m. 0,5 Sulfur (S) % d.m. 0,2 <0,3 Chlorine (Cl) % d.m. 0,5 <0,8 Fluorine (F) % d.m. 0,0 <0,05 Mercury (Hg) mg/kg d.m. 0,4 <0,5 Cadmium (Cd) mg/kg d.m. 1,6 <2,0 Sum of other heavy metals 1) mg/kg d.m. 490 <750 1) Sb, As, Cr, Co, Cu, Pb, Mn, Ni, V
Currently there is no standard that would directly relate to a certain fuel category or level of trace elements. There is though the German fuel quality key that to a fair extent describes, qualita tively, the fuel origin. A quantitative key is yet not there.
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Starting 2001 with the new biomass law in Germany many 5 - 20 MWe power plants based on demolishing wood where planned. Some of these had as goal a high power plant efficiency and therefore a need for high steam parameters. Examples of this kind of plants now in operation or near commissioning are: Heizkraftwerk Kehl 44 MWt 500 °C 90 bar 2003 Prokon Nord Energiesysteme 62 MWt 500 °C 90 bar 2003 MVV Energie AG, 55 MWt 480/487 °C 90/16 bar reheat 2003 Königs Wusterhausen The business concept chosen by the investors for these plants is power generation, selling the electricity to the grid and benefiting from the renewable energy law subsidy. The need for high efficiency comes from the already rising price of fuel. Demolishing wood has become a com-modity in Germany, and thus also in neighboring markets that previously purchased cheap de-molishing wood from German suppliers. The INTREX TM concept provides a good basis for this type of high efficiency plant with minor risks for corrosion. Emission limits are according to the strict limits of the German 17.BImSchV. Permitting is basi-cally done based on the temperature and prevailing time requirements of this law, that was specified based on grate firing boilers for municipal solid waste. Thus permitting for CFB boilers according to 17.BImSchV is based on case by case exceptional permits from the authorities. Currently the standardizing work is ongoing to get a common ground more directly related to the technology represented by the fluidized bed boilers. The differences for Hornitex plants are the higher steam parameters and that the bigger IN-TREX TM super heater is divided into two sections. The Kehl plant was commissioned in the be-ginning of this year and handed over to the customer according to the schedule in March 2003. The emission limits were met with good margins. The plant is now in commercial use since March 2003 as a first plant following the rules of the German biomass law. The Prokon Nord 20 MWe boiler plant in Papenburg is a very similar plant compared to Kehl boiler. The Papenburg plant will burn also demolition wood in categories A1-A4. The plant will be commissioned in May-June 2003 and handed over to the customer in September 2003. An other development step was made in fluid bed technology for biomass when Foster Wheeler agreed with MVV Energie AG Mannheim of a delivery of a 20 MWe power plant to Königs Wusterhausen near Berlin. MVV targeted directly for a high efficiency plant and it is the first 20 MWe reheat, biomass power plant with parameters 480/487 °C, 90/16 bar, 17.7/16.2 kg/s. The plant is approved according to 17.BImSchV and will burn demolition wood in categories A1-A4. Because of the high parameters the plant has a gross efficiency of 36.4 % compared to the minimum of 29 % according to the biomass law. The plant will be commissioned in May-June 2003. This plant is until now the only reheat biomass plant in this range. The combustion con-cept is the same as in the Kehl and Prokon Nord plants but only the final superheating and re-heating occur in the INTREX TM heat exchanger. The plant also has the same type of open step grid as in the other demolition wood plants.
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Picture: MVV Königs Wusterhausen 20 MWe EPC plant There has been a great interest in the Königs Wusterhausen plant because of the reheat con-cept and the high efficiency. The fuel prices have changed rapidly upwards during the construc-tion period of the plant and it seems that the last biomass plants will have more interest in simi-lar concepts. Finally we may say that the way from bark fired boilers to demolition wood boilers has deve l-oped step by step, but we feel to day very comfortable with the concept for demolition wood burning and it is really possible to build a reliable plant with high efficiency, Reisezeit >8000 h and availability > 91%. An other application using the same concept is the bio mass power plant for untreated wood. These plants target for high efficiency and high availability and gives the plants the basis to use more valuable fuels. Examples of this type of plants: Jämtkraft , Östersund 125 MWt 545 °C 145 bar wood resid. 2002 Mälarenergie, Västerås 157 MWt 540/540°C 171/40 bar wood resid. 2001 Lycksele 46 MWt 520 °C 87 bar wood resid. 2001 There is a certain interest in Germany now also in this type of plants of untreated wood because it seems to be easier to receive fuel agreement with this more valuable untreated wood.
6. The CFB with Intrex™ superheater and W-T-E concept for RDF As the once opportunity fuels become traded commodities with initially rising fuel prices the search for further opportunities continues. A shift was seen to plants adding to their basic demo-lition wood menu, a flavor of RDF. This refuse based fuel could be derived from municipal or commercial sources. Process changes are then needed again to cope with the changed conditions, higher chlorine content and except trace elements of heavy metals also a massive presence of alkalizes. This is however not enough. Also mechanical changes are needed because of impurities in the fuel,
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which cannot be fully avoided by upstream measures like magnets and eddy current separators for nonferrous material. Basis for the design is to some extent features from the demolition wood plants, with changes: Mechanical fuel feeding spring hammer soot cleaning material changes extraction of tramp material Process steam temperature and pressure 480 °C/ 65 bar super heater arrangement empty pass changing conditions in the backend The fuel with the higher amounts of impurities is even more heterogeneous, depending heavily
on source and not standardized but supplier specific to a certain extent. It can well be seen that apples are not like other apples even if they still are fruit – and the usual numbers tentatively describing the fuel can become problematic und insufficient.
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Rest % 1,3 Total % 100
The above figure and table describe briefly that the chosen pathway, source and technology may largely affect the outcome and resulting fuel. Also it must be pointed out here how difficult it is to make representing sampling for such heterogeneous fuel and consequently describing it in numbers is very difficult. A major difference is whether the fuel is source sorted like DSD in Germany and e.g. common in parts of Scandinavia, or if it is fuel derived from unsorted solid waste. Examples of Foster Wheeler boilers that burn RDF type of municipal and industrial solid waste are: Stockholm Energi AB Högdalen, Sweden 91MWt 480 °C 60 bar 2000 Lomellina Energia, Italy 59 MWt 399 °C 62 bar 2000
Picture: Högdalen RDF plant
Problems that must be countered are fouling and corrosion, but on an entirely different level than in demolition wood fired boilers. This may be seen also in the picture below.
CIRCULATING FLUIDIZEDBED BOILER91.2 MWth, 31.8 kg/s, 59 bar, 480°C
STOCKHOLM ENERGI ABHÖGDALEN, SWEDEN
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This will evidently also together with the mechanical properties have an influence
on availability and Reisezeit, the impact however that must be minimized through the proper countermeasures. The quest for availability is based on plant design; fuel selection, preparation and feeding for homogeneity and quality; process control and data sampling and analyses. Now the control of the boiler is further enhanced and the SmartBoiler™ platform provides an excellent toolbox to master combustion of fuels with high fouling and corroding tendencies but also serving broader purposes. Some of Smartboiler™ :s features are: online corrosivety measurement and action fouling control bed condition emission optimization E.g. the corrosivety measure goes far beyond the scope of a simple online HCl measurement. The corrosivety is a complex function of different flue gas elements like alkalis, heavy metals, sulfur or lack of sulfur, silica reactions – HCl is really not the essential problem but many other chlorine compounds are.
PowerGen Europe 2003 Conference, Düsseldorf, Germany, 6 – 8 May, 2003
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7. Current market situation & trends The current activity especially on the German market is on the sinking edge of the demolition wood crest, with some plants still to be agreed before June 2004 including also some biomass plants for clean wood and for other biomass fuels, but emphasis and resources clearly being shifted towards RDF and the EU directive preventing land filling of combustible waste after 2005. This wave will keep investors and suppliers busy for a while, but what comes then. In the wake of the investments the plants already built must also be run, and making money. Changing conditions in the maturing but dynamic fuel market may be a fortune for some operators, caus-ing pressure for others. Flexibility is one strategy, strong niche positions another. Opportunity fuels based on e.g. local conditions (also cogeneration to be mentioned) but also larger trading and transport may remain as an important flavor on the market. Different waste streams may arise and gain focus either locally or on a broader scale. In the end of the day it may be stated that a rich mix of available, installed technologies each fit for it’s purpose may prove a higher than anticipated strength for the EU. The market will keep changing at least for some years to come, and thus the adaptation may follow with mostly incremental and minimized investment. This could be seen as a disadvantage for equipment suppliers, but in the end it is still a benefit for the common layers. There is a big market for different biomass plants in Europe. Continuously there will be new biomass fuels, which are offered to the plants. There will be certainly also space for different plant technologies. Partly the fuels will be more demanding which need mechanical or process changes in technologies, which development has been going on also the past twenty years. Fluid bed gasifying is probably a technology, which will have a breakthrough both using biomass and also RDF type fuels. Gasifying can be a solution to handle many fuels, which were until now difficult to use with traditional methods. For Biomass there will be totally perhaps some 25-30 plants built in Germany according to the biomass law until end of 2005. The assumptions promise a total amount of some 5 million tones RDF annually in Germany, which would be enough for some 20 to 25 new RDF plants for the coming years. The trends are similar in other European Union countries but only depending on the local subsidies . The fluid bed technology will have a challenge for coming years in different kind of applications which are based on the above mentioned boiler technology:
• Biomass plants for untreated wood and connected to district heating with high efficiency especially in Scandinavia, but also in Central Europe
• Demolition wood based power plants in central and southern Europe with high efficiency
and subsidized electricity price
• Plants for new biomass fuels, agro-wastes partly with modified technology
• The RDF – sludge- paper waste combination e.g in European pulp and paper mills but also municipalities and based on new waste directives
• Different sludge’s combined to other wastes incinerated as waste disposal
• Operational support from different O&M monitoring systems to support the demands for high efficiency and availability.
