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HomeMy WebLinkAboutPeat Resource Estimation in Alaska Final Report Vol II November 1980PEAT RESOURCE ESTIMATION IN ALASKA 002 FINAL REPORT Prepared by: EKONO, Inc. 410 Bellevue Way SE Bellevue WA 98004 Under Contract to: State of Alaska Department of Commerce and Economic Development Division of Energy and Power Development 338 Denali Street Anchorage AK 99501 5 Prepared for: US Department of Energy Division of Fossil Energy Grant No. DE-FG01-79ET14689 This report was prepared as an account of work sponsored by the United States Govern- ment. Neither the United States nor the United States Department of Energy, nor any of their employees, nor any of ther con- tractors, subcontractors, or their employees, make any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product, or process disclosed or represents that its use would not infringe privately-owned rights. TABLE OF CONTENTS Page SUMMARY 1 1, CHARACTERISTICS OF PEAT FOR ENERGY PURPOSES 2 1.1 Degree of Decomposition 2 1.2 Bulk Density 2 13 Impurities 2 1.4 Volatile Content 3 1.5 Ash Content 3 1.6 Moisture Content 3 1.7— Heat Value 5 1.8 Flue Gas Volume 5 1.9 Ash Fusion Characteristics 5 2. HARVESTING OF PEAT 8 2.1 Dry Methods 8 2.1.1 Milled Peat Method 8 2.1.2 Sod Peat Method 10 2.2 Hydraulic Methods 11 2.3 Combined Methods 13 3. ENERGY CONVERSION OF PEAT 14 3.1 Direct Combustion 14 3.1.1 Pulverized Firing 14 3.1.2 Combustors ‘ 14 3.1.3 Grate Firing 17 3.1.4 Applications to Existing Systems 7 Wwwww w . . . . . mm Mm Mm MO MP . . . . PPP PP HHH LP er ee ee ee Pwr — NON NYONN | — — -e 8 lee oe annn o 8 © 6 PwWwnr — TABLE OF CONTENTS Processing Briquetting Wet Carbonization Biogasification Gasification TECHNICAL VIABILITY OF PEAT UTILIZATION Space Heating Individual House Heating -Centralized Heating Power Generation Small-Scale Steam Cycles Large-Scale Steam Cycles Gasification for Small-Scale Power Generation Gasification for Large-Scale Power Generation ECONOMIC VIABILITY OF PEAT UTILIZATION Price as a Fuel Cost of Heat Generation from Peat Cost of Power Generation from Peat 18 18 18 18 19 20 20 20 20 23 23 23 25 26 27 27 27 28 LIST OF FIGURES MOISTURE LEVELS IN PEAT EFFECT OF MOISTURE CONTENT ON HEAT VALUE OF PEAT FLUE GAS VOLUME, SCFT/10°BTU FUEL SYSTEM OF A PEAT FIRED BOILER PULVERIZERLESS FUEL SYSTEM OF A PEAT FIRED BOILER HOME HEATING FURNACE FOR SOLID FUELS A COMMERCIALLY AVAILABLE PEAT-FIRED BOILER PLANT | HANDLING, STORAGE AND BURNING SYSTEM OF MILLED PEAT LIST OF TABLES PRICES OF PEAT BASED FUELS IN 1980 HEAT GENERATION COSTS FROM PEAT IN 1980 POWER GENERATION COSTS FROM PEAT IN 1980 CHARACTERISTICS OF PEAT FIRED PLANTS Page 15 16 21 22 24 Page 27 28 28 29 SUMMARY This document was prepared to support all potential efforts to utilize the Alaskan peat resource as a fuel. Volume I of this report concen- trates on the characterization and evaluation of the resource itself, while this volume discusses the fuel characteristics of peat in terms of their effect upon the equipment. Current and future peat harvesting methods are described, and their applicability to Alaskan conditions is estimated. The state-of-the-art of both direct combustion and processing methods are discussed prior to the presentation of the actual equipment avail- able for peat based space heating or power generation. Finally, the current costs of peat, peat derived fuels, and peat derived energy are presented, ready to be compared with competing energy costs of today or of the future. 1. CHARACTERISTICS OF PEAT FOR ENERGY PURPOSES 1.1 Degree of Decomposition The main parameter from the fuel point of view is the degree of decomp- osition. It determines the heating value, volatile content, and bulk density, which in turn are the main parameters in the design of facil- ities for energy conversion and handling. Generally, a higher degree of decomposition indicates good fuel peat potential, provided that other parameters are positive. By experience, grass peats (Carex) can be allowed a lower decomposition degree than moss peats (Sphagnum), mainly because they dry faster. In principle, a weakly decomposed moss peat is unsuitable for fuel peat production. This is true for the whole bog, if there is a layer thicker than one foot of low-grade moss peat. On the other hand, it would make excellent horticultural peat. Peats with a low degree of decomposition dry generally faster, which also determines the number of harvests per season in current production methods. In Northern conditions, medium decomposed peats are optimal for fuel purposes. 1.2 Bulk Density The bulk density of peat is an important parameter as it affects the transport and handling costs, as well as the energy storage capacity at the plant. Aged, medium decomposed peat is denser than young peat from the surface of the bog. Not only is it more economical to transport, it also contains less impurities and causes less difficulties in conveyors and storage bins. The density of good fuel peat exceeds 22 1b/cuft. 1.3 Impurities Mechanical impurities are problematic in all phases of peat utilization. Peat contains wood in the form of roots and sticks; it may contain rock from ditching operations and metal parts from machinery. Winter condi- tions may induce snow and ice chunks into the peat. A proper equipment to homogenize the fuel at the plant is very significant. 1.4 Volatile Content The content of volatile matter, as obtained from the proximate analysis, is a significant parameter in the design of combustion or processsing equipment. It determines the volume and speed of the volatilization process, which is an early part of all energy conversion processes. The visible effect in the combustion of peat is a long luminous flame that requires a large furnace. 1.5 Ash Content The ash content in good fuel peats can be as low as 5%. Peats with an ash content up to 11% are in regular use as a fuel. From the firing design point of view, ash contents up to the 25% range do not prevent the use of peat, but they must be carefully taken into account. In any case, the ash represents an additional ballast in handling and an. increas- ed volume of erosion in all parts of the system. 1.6 Moisture Content The most difficult technical obstacle to utilizing peat as an energy source is the reduction of the associated large water content. Natural peat is approximately 90% water. In this condition, the heat of combus- tion of the solid matter is less than the heat of vaporization of water. Figure 1 shows the reduction in water necessary to achieve an acceptable feedstock for energy utilization. The peat-water affinity is due to several factors, e.g., colloids, hydrogen bonding, etc. The currently used commercial harvesting processes rely on solar and convective drying, a slow and uncertain process that limits harvest to a period that is often very short. It must be recognized that mechanical dewatering methods can currently reduce the moisture content down to about 70% and that the foreseeable development in that area will not provide fuel directly applicable to combustion or gasification. Current harvesting methods produce fuel at a moisture content of 30-55%. From that delivery state, the actual combustion process requires a further reduction down to 10-25%, depending on the configuration. Different firing methods accomplish this in different ways, as will be discussed later. -3- 100 90 80 70 60 50 40. %, MOISTURE REMOVAL 30 20. 10° ja— ACCEPTABLE FEEDSTOCK . FOR ENERGY UTILIZATION ©00 EEA EKONO Inc. CONSULTING ENGINEERS BELLEVUE , WASHINGTON, U.S.A. 10 20 30 40 50 60 70 80 90 100 ~% MOI STURE ‘py! LEVEL IN BOGS FIGURE 1. MOISTURE LEVELS IN PEAT CLIENT PROJ. NO. PROJECT NO. ee FORM NO. 16 LB H,0/LB PEAT 1.7 Heat Value The heating value is a steep function of the moisture content, because the water to be evaporated requires part of the heat from combustion. This is illustrated in Figure 2. Ash content simply reduces the amount of combustible matter, thereby inducing a proportional decrease in the heating value. 1.8 Flue Gas Volume The specific flue gas and combustion air volumes per a unit of released heat are higher for peat than most other fuels, excluding wood, as can be seen in Figure 3. This affects the design of the boiler and all gas handling equipment, as will be discussed later. 1.9 Ash Fusion Characteristics Ash fusion temperatures and an ash analysis are necessary in order to aid in predicting the slagging and fouling characteristics of the peat. Slagging is the accumulation of plastic or liquid deposits of ash on radiant heat exchange surfaces in the furnace. Fouling is the accum- ulation of deposits on boiler tubes. Both slagging and fouling can lead to loss of boiler efficiency and to unacceptable downtime. 10,000 9000 8000. 7000 lu 3 ae 6000 >a ot eee Eo 5000 <cwm e 4000 3000 2000 * 1000 0 -1000 000 [4 EKONO Inc. CONSULTING ENGINEERS BELLEVUE , WASHINGTON, U.S.A. HIGHER HEAT VALUE NET HEAT VALUE SOD PEAT] |MILLED PEAT % MOISTURE IN PEAT FIGURE 2. EFFECT OF MOISTURE CONTENT ON HEAT VALUE OF PEAT ico BY: ss DO BY: REV. BY: REF. OWG. eee +—____ cones FORM NO.I6 EXCESS AIR COEFFICIENT —/ 7 SPECIFIC FLUE GAS VOLUMES FOR VARIOUS FUELS SPENT ‘SPENT —— . PEAT WOOD WASTE LIQUOR. LIQUOR - NATURAL — BITUMINOUS(MOISTURE) (MOISTURE) Mg Ca GAS HEAVY COAL (4) (%) (D.S.) (255) FUEL OIL 55 50 45 65 60 55 55°60 55°60: meaner tone 0» CONTENT OF FLUE GAS (2). - 2a HARVESTING OF PEAT 2.1 Dry Methods All current methods to produce fuel peat in quantities can be classified dry, i.e., their use is preceded by the drainage of the deposit. There are two methods, with the main difference in their volumetric capacity: milled peat method and sod peat method. The preparatory measures in common for both and the methods themselves are discussed in the fol- lowing: 2.1.1 Milled Peat Method Milled ridge peat harvesting is based on the air-drying of a fine sur- face layer of fluffed peat to roughly 55% moisture content and ploughing into strings (ridges) in the centre of the production fields. The ridges of peat are then transported, by various methods, to either a bogside storage facility or directly to a thermal power plant, or other users. The first operation profiles the fields such that they slope at ap- proximately one in twenty towards a drainage system, which assists the surface runoff of rain water during the production season. After this operation has been completed, the first operation in the production cycle is the milling of the surface layer of peat to a depth of ap- proximately one-half of an inch. This layer is then left to dry until it has reached approximately 65% moisture content at the surface. This is usually accomplished within one day. Once the top of the milled layer is air-dried to 65% moisture content it is turned over by a spoon harrow to expose the underside of the surface layer to air-drying. It can take several harrowings and a period of two to three drying days to lower the moisture content to approximately 55% and extra harrowing may be required if rain intervenes during the drying process. os Once the moisture content of the peat has dropped to approximately 50- “55%, the surface layer is ploughed into ridges in the centre of each production field, which can then be handled by larger capacity harvest- ing equipment. Finnish peat producers average 16 harvests or passes per season. Table 7 of Volume I lists estimated numbers of harvests for selected Alaskan regions, ranging between 10 and 16. The two principal methods for transporting peat from the production fields are the so-called Peco and Haku systems. Both systems utilize similar pieces of equipment but transfer the peat differently to the storage piles. The milled vacuum peat harvesting method is similar to the previously described milled ridge method except that the collection methods for the peat differ. In the vacuum peat production the air-dried surface layer is collected by a vacuum collector using front or side-mounted air suction nozzles. A milling device is usually towed behind the unit to prepare the next surface layer. The air dried peat then passes through a cyclone where it is settled into a storage tank. The tank, located under the cyclone is side-dumped into a storage pile at the end of the field. From there the peat is transported by conventional trailers or dumpers to the final storage area. The milled vacuum peat mining method completes several operations in one cycle, namely; milling, harrowing, harvesting, stockpiling and transportation. Usually a single harrowing is sufficient to dry the thin layer of peat to the required 55% moisture level. Vacuum collection can result in a reduction of the drying cycle from two or three days to one day when compared with the ridge method. This is achieved because only the drier peat particles are picked up by the vacuum collector as it passes over the fields. The moisture content of the collected peat can be controlled by adjusting the ground clearance of the vacuum nozzle. The surface layer picked up by this method is approximately one-quarter of an inch on average, but is not as even as in the ridge method. Field production stockpiles are located at the end of each field. As in the ridged peat production method the stockpiles are compacted and sometimes covered with thin plastic to protect the peat from moisture build-up, wind loss and spontaneous combustion. The piles measure 10-20 ft in height and vary in length. : The peat is transported off the bog to central storage piles by a special transporter or wagon. From these piles the peat can be loaded, as required, to either conventional rail or truck systems for transport to the end user. Where a thermal plant or other industrial centre is located adjacent to the bog, peat is usually transported from the field storage piles to a permanent storage facility at the plant. 2.1.2 Sod Peat Method The sod peat production system is based on air-drying blocks of peat which have been cut from the bog and mechanically extruded or stacked on the surface of the bog to dry. Specialized equipment has been designed to cut vertically into the surface of the peat to macerate the top layer and extrude either blocks or rolls of solid peat onto the surface of the bog to be air-dried. The total sod peat production cycle involves clearing, peat cutting, windrow preparation and transportation of peat. The first stage of the cycle is to clear the surface of loose mossy peat and prepare it in an even fashion for the sod peat cutter to pass over during the production cycle. To accomplish this, a screw cutter or profiler machine is used to level the surface of the fields. In Ireland a continuous bucket excavator and macerator, mounted on wide tracks, is used to cut and extrude blocks of peat onto a spreader which lays the peat blocks in an orderly fashion for air-drying. Macerating helps to mix the surface layers of peat with the more decomposed bottom layers of peat. The maceration of the peat compacts the extruded material and, once dried, the peat is more impervious to moisture build-up. In Finland, sod peat cutting is used only when milled peat methods are not -10- _technically feasible due to the nature of the deposit. The Finnish sod machine produces sods with a diameter of 2-4 inches by extrusion of peat through nozzles in the rear of the cutting machine. The cylindrical sods are left on the surface of the bog for air-drying until they have approximately 75% moisture content, at which them they are stacked into windrows to continue the air-drying process. From this stage on, the sods are fairly insensitive to rain. The preparation of windrows is necessary to clear the bog surface for the next production cycle while allowing the peat to continue air- drying. A specially designed plough is used to lift and turn the sods as it piles them into windrows. After the upper layer of the windrows has dried to 55% moisture content, the same machine is used to turn over the windrow to permit the sods in the lower portion of the piles to be exposed to air-drying. After additional drying days, the windrows are ploughed and turned by a collecting machine which gathers the sod peat for loading and transport. Smallest sod peat machines are designed to be driven by a farm tractor. They are capable of producing peat to cover the energy demand of a small community at a minimum of investment cost. Given the prevailing abun- dance of bog areas compared to the local demand in Alaska, and the relative insensitivity of sods to rewetting, the sod peat method seems to have the greatest potential to be used for Alaskan communities. 2.2 Hydraulic Methods The hydraulic harvesting method is an alternative which may become more attractive in the future for fuel peat production if certain technical problems associated with it can be resolved. As this mining method does not rely on solar drying, it is therefore, to a large extent, independent of climatic conditions and can be used in many regions where peat production was not thought to be possible. -11- _ In principal, a hydraulic peat mining system follows four steps: - dredging of raw peat from an unprepared bog; - the preparation of peat slurry; - the pumping of this slurry to a dewatering plant; - mechanical dewatering of the slurry to an acceptable moisture content. The first 3 steps are not only technically feasible, but are also relatively low in cost, however, the mechanical dewatering operation is technically unproven for use on fuel peat production. During the past 30 years, many mechanical systems have been tried with varied results. Geneally speaking, those systems which were successful in dewatering peat to 50% moisture content, operated at such a low capacity that commercial production quantities were economically unrealistic due to the large amount of equipment necessary. Conversely, those systems with a higher production capacity could only lower the peat moisture content to approximately 70%. The problem associated with the mechanical dewatering of humified peat is related to the colloidal content of the material, a problem which exists in many other industrial and chemical dewatering processes. The most recent mechanical dewatering equipment trials have been conducted by Western Peat Moss Company, Limited in Richmond, British Columbia. The trials were based on modified variable pressure nip twin roller presses which were originally designed for sludge dewatering. Preliminary results from the equipment trial held in April 1978 indicate that mechanical dewatering of moss peat to 70% moisture content can be achieved on a high capacity basis. While peat at this moisture level is not usable as fuel for power generation, it is close to the maximum acceptable level of 65% currently practiced in European operations. -12- Zia Combined Methods A combination of hydraulic collection and sod drying would also combine some of the advantages of both approaches, mainly the short lead time and environmental acceptability of hydraulic methods and the relative insensitivity of sod peat method to climatic conditions during the drying period. The method would include hydraulic collection, pumping to firm ground, sodding and spreading of sods to drying fields, plus drying, collection and stockpiling as in the sod peat method. The combined method offers considerable potential in regions, where bogs are confined, but surrounded by dry vacant areas. Thus the small bog area would be dedicated to peat extraction only while the specialized drying area would effectively determine the yield of the combination. Some areas in the interior of Alaska have characteristics that would favor this method. -13- 3. ENERGY CONVERSION OF PEAT Sul Direct Combustion 3.1.1 Pulverized Firing The most suitable form of peat firing in large power boilers is sus- pension firing of pulverized peat. Before the final introduction to the furnace peat must be dried and equalized in one or more stages. Chunks of wood, always present in peat, must be screened out and eventually crushed to be returned to the final flow. The drying from the 40 to 55 percent moisture of delivery state to 10 to 25 percent residual moisture of firing state, is realized using either recirculated flue gas or hot air. When ordinary pulverizer equipment is used (Figure 4), the drying takes place in the pulverizer and the peat-gas suspension is blown to the burners. The pulverizers used are of hammer or beater type, either combined with a blower wheel or equipped with a separate fan. One of the recent improvements has been the dropping off of the pulveri- zer. In this system (Figure 5), peat is dried in a flash dryer and blown to the burners with primary air. This method, as described, has the additional advantage of not reducing the steam capacity of the boiler, because the voluminous dryer gases are not led to the boiler, but directly to the stack. Furnaces fired with pulverized peat need a burnout grate at the bottom of the furnace due to incomplete pulverization of larger wood particles in the fuel. Narrow traveling grates and stationary grates with dumping grate sections are used. 3.1.2 Combus tors The prevailing type of combustors used for peat firing is the cyclone. Many cyclone installations are plagued by the instability of the slag. Dry cyclones tend to have slag meltdown when the peat is dry, and wet -14- -SL- AIR INTAKE | STACK | SILO 2 y F. D. FAN omminmnK®, 4), (tes Feeder | os, Fie ELECTROSTATIC PRECIPITATOR PULVERIZER WET SLAG CONVEYOR FIGURE 4. FUEL SYSTEM OF A PEAT FIRED BOILER -9L- AIR INTAKE DUST COL- LECTOR LS 2 2 STEAM BOILER(S) AIR PRE- HEATER CONVEYOR FAN FIGURE 5. PULVERIZERLESS FUEL SYSTEM OF A PEAT FIRED BOILER bottom cyclones experience slag solidification when very wet peat or ice chunks are introduced. Both vertical and horizontal cyclones are used. The fluidized bed combustor is a versatile one and can well be used for peat. It is flexible in its behavior with respect to the fuel quality, but one of its major advantages, the sulphur removing capability, is not needed. 3.1.3 Grate Firing Most types of grates are applicable to peat firing, ranging from small central heating furnaces to medium size utility boilers. Grate firing system is a relatively simple one, since it incorporates the drying phase of the fuel to take place on the grate. Design parameters and operational practices are different from other fuels, however. For example, the free grate area must be kept lower than other fuels, 4 to 8 percent in inclined grates and 12 to 18 percent in traveling grates to avoid crater formation and consequent flyash blow-away. The same purpose leads to high fuel layer thicknesses, up to four feet on travel- ing grates and steeper angles of inclination with inclined grates. The problem is not only the fouling of boiler passes nor increased particle emission, but specifically an increased danger of a dust explosion in the furnace. The temperature of primary air and the overall thermal load must be kept low in order to avoid ash fusion, which, amongst other inconveniences, also leads to extreme wear of moving grate parts. 3.1.4 Applications to Existing Systems Co-firing with other fuels would be the easiest case to substitute peat for more expensive, scarce, corrosive or polluting fuels in an existing boiler without significant retrofit measures. Peat may easily be added to hog fuel or coal in grate firing, fairly independent on the grate type. Best results have been achieved with the so-called sandwich firing where the peat layer is introduced onto the coal layer on a traveling grate. -17- The low fusion temperature of typical peat ashes is a problem that occurs in many cases of co-firing. The inherent high temperature of an oil flame poses an obvious danger, but even co-firing with coal ona grate with preheated primary air may cause problems if the quality of peat is not consistent. 3.2 7 Processing 3.2.1 Briquetting Many smaller-scale firing and gasifying techniques require that milled peat be pressed into suitable sizes of briquettes. For that, the peat must. be homogenous as to moisture content, density and fiber content. The briquetting involves thus blending, crushing and screening before drying to a moisture content of about 10% and final compaction. The heat required by the dryer may conveniently be generated from combustion of rejected fibers. 3.2.2 Wet Carbonization This process overcomes the time consuming air drying on the bog, because the peat slurry can directly be led through pulping, screening and preheater stages to a steam-heated reactor. The carbonization process takes place at elevated temperatures and pressures, whereafter the matter is filtered, flash dryed and pelletized. The heat required by the dryer and the reactor is generated by firing a part of the product. The efficient heat recovery may keep this portion as low as 27%, even lower if rejected fibers are used. 3.2.3 Biogasification Dewatering is not required in this process, where the peat slurry is first partially oxidized and then fermented by bacteria in an anaerobic biological reactor. The resultant methane gas must be cleaned of carbon dioxide and other ballast gases. The bacteria is maintained by adding controlled nutrients. The process is still in the laboratory-scale research phases. -18- 3.2.4 Gasification Peat is very reactive during gasification, and integrated processes yield low or medium Btu fuel gas, synthetic gas, fuel liquids and ammonia with less sulphur by-products than coal. The product mix can be varied significantly by controlling gasification temperatures and pressures. Different basic types of gasifiers can be used, including entrained flow and fluidized bed gasifiers. Downstream units would include equipment for heat recovery, gas quench, acid gas removal, water gas shift, and methanation, depending on the composition of the raw gas and the desired gasification product. Energy efficiency and process cost considerations require, however, that peat be dewatered to 50% moisture content at the maximum, often lower. / -19- “4, TECHNICAL VIABILITY OF PEAT UTILIZATION 4.1 Space Heating 4.1.1 Individual House Heating A supply of peat or peat products like briquettes provided, a variety of peat fired furnaces is available for home heating purposes in Finland and in Ireland. The technology could also be easily transferred to the newly-emerging U.S. furnace industry. Figure 6 shows a typical sod peat, briquette, wood chip, or straw fired home heating furnace with a heating capacity of 25 kW (290,000 Btu/hr). It is thus capable of heating a large house or duplex or a small industrial or commercial structure. Due to a large fuel hopper, it needs refueling at intervals of 1-3 days only. The firing can be automatically shifted to back-up oi] when peat is exhausted from the hopper. Peat briquettes can be used in smal] wood stoves much like firewood, but being more difficult to ignite and producing higher combustion temperatures that may be hazardous to the grate. 4.1.2 Centralized Heating The choice of available hot-water boilers for centralized heating of several houses or apartment buildings becomes more comprehensive with the increasing capacity. Heating plants between 1 and 5 MW (3 and 15 million Btu/hr) normally use simple stationary grates with underfeed or overfeed stokers while larger plants up to 20 MW (70 million Btu/hr) can afford more elaborate mechanical grates that allow the use of milled peat in a well-controlled manner (Figure 7). -20- Tekniset_ tiedot polttoaine: palaturve, briketti, puu, olki teho 25 kw kaytto: 3 - amakotitalot 300-1000 m - hallit 4000 wm Helposti autamatisoitavissa si- ten, ett turpeen loppuessa sii- losta linmitys siirtyy sdhkdlle tai dljylle. Hoitovadli turvetta kaytettiessa 1-3 vrk FIGURE 6. Specification fuel: sod peat, briquettes, wood, straws capacity for use: 3 - houses 500-1000 m 3 - industrial halls 4000 m The equipment is easy to auto~ matize so that as soon as the peat is exhausted fram the silo the heating is continued with electri- city or oil. Attendance with peat fueling at 1-3 days intervals HOME HEATING FURNACE FOR SOLID FUELS -22e- PEAT-FIRED BOILER PLANT |. FUEL BIN 6. AIR PREHEATER 2. BIN DISCHARGER 7, DUST COLLECTOR 3, FUEL FEED 8. STOCK: 4. GRATE 9. ASH REMOVAL 5. BOILER ‘ FIGURE 7. A Commercially Available Peat-Fired Boiler Plant h 4.2 Power Generation 4.2.1 Smal1-Scale Steam Cycles Small peat fired steam cycle plants use same kinds of firing equipment as large heating plants, but adapted to a steam boiler that generates steam for the prime mover. The selection of firing equipment depends on the form and quality of peat to be fired. All the components of the small-scale steam cycle generating system are proven and commercially available, but seldom combined as a plant. The reason is that the economies of scale are very steep, and all other forms of energy have been more competitive either in terms of technical or of commercial viability (or both). The main problem area is the prime mover, which either has a very low efficiency or requires high steam parameters (pressure and temperature), thereby making all steam related components, especially the boiler, more expensive to invest and operate. Two types of prime movers are applicable: steam turbines and steam engines, both of which have been used for decades in various services. The applicable sizes range up to 500 kW for steam engines, while steam turbines range from about 100 kW up. The thermal efficiency of a plant can be as high as 80-85% if the principle of cogeneration can be used, i.e., the steam from the turbine exhaust can be used for industrial processes or district heating. If condensing generation must be used, the overall efficiency of a plant of this size is 20-25%. 4.2.2 Large-Scale Steam Cycles The major share of fuel peat consumption in the world is being fired in medium and large conventional steam boiler and turbine generating plants with capacities ranging between 30 to 700 MW (Figure 8). Milled peat is used in pulverized firing to generate high-pressure steam to drive steam turbine-generators. Either cogeneration or condensing power -23- -v2 - (13000 m3) (2x3,5t ) (250.600 m3/h ) (600 m3/h) ( 100 m3/h ) (50...100 m3/h) (600 m3/h) (100 m3/h) ( 600 m3/h) { 250 m3/h) ( 600 m3/h) Receiving station of milled peat Belt conveyor to the roof of the power plant net for removal of iron conveyor on the roof of the power plant and belt balance (250 m/h) Distribution silo Sax-rotor discharger Screw discharger Feeding silo Feeder of milled peat Crusher of milled peat Fan for milled peat Steam boiler {250 m/h) Belt feeder ( 41kW Screening device Belt conveyor tor stumps Crusher for stum Belt conveyor af Belt conveyor after the crusher Belt conveyor Belt conveyor Belt conveyor to the storage silo Distribution belt conveyor on the storage silo ( 600 m3/h}) Storage silo Movable screw discharger Belt conveyor under the storage silo Belt conveyor from the storage silo 130 m3 ) (3.140 m/h {3x 48,5 m (3x12...40 t/h (3 x 200 kw (82800 mn 7h} (83 kg/s, 113 bar, 535°C ) Electrostatic precipitator (collector efficiency 98%} (2x 360000 m3n/h) (H=90 m) S fer the screening device (3500 m?) 250 m3/h) ( 250 m3/h) Flue gas fan (250 m37h) DAFON=OCOBVIBUFLWN— ii =&xono CITY OF TAMPERE ELECTRICITY WORKS NAISTENLAHTI UNIT No, 2. COMBINED HEAT AND POWER PLANT Handling, Storage and Burning System of Milled Peat “8 JuNdI4 generation can be applied with the same basic differences as above. Due to higher applicable steam parameters, a condensing plant can obtain a 35% overall efficiency in this scale. A favorable combination of a fuel resource, power demand, and especially of thermal energy demand in cogenerating cases is required for a feasi- ble operation. This is due to the extreme transportation intensity of peat, which limits practical transportation distances to about 50 miles by truck and 100 miles by rail. If coal is available within a radius of at least 150 miles, it would probably be more competitive. 4.2.3 Gasification for Small-Scale Power Generation Laboratory and pilot-plant scale experiments on peat gasification equipment have been and are being run in several countries. Gasifiers are usually modified wood or coal gasifiers producing low Btu gas. The heating value of the gas is highly dependent on the moisture content of the peat feedstock and should not be higher than 30% in most cases. Few experiments using peat gas as a fuel for internal combustion engines have been made. Some effort has also been dedicated to transfer the experience from biomass gas fueled engines to peat, because the gas is fairly similar. Gasoline engines are known to lose as much as 50% their power on peat gas, while diesel engines lose about 10-20%. Due to the physical limitations originating from the large volume and other un- favorable properties of the gas, gas is better applied to larger low and medium speed stationary engines than to small high-speed automotive engines. The gas must be purified and cooled before it is introduced into the engine. For a successful application, the moisture content of the feedstock must be below 25%. Gas turbines seem to be more sensitive to the composition, purity, temperature, and pressure of the fuel gas than diesel engines. It is therefore probable that the gasifier should be preceded by another processing unit, like a wet carbonization plant to maintain the quality of the gas. Possible combinations and their feasibilities are being studied at the moment. -25- 4.2.4 Gasification for Large-Scale Power Generation Gasifier equipment is subject to very steep economies of scale. Medium- size plants are therefore not being developed, but ongoing programs funded by DOE concentrate to large plants for SNG production. The gas could be used like natural gas in any application, including large generating stations. -26- 5. ECONOMIC VIABILITY OF PEAT UTILIZATION 5.1 Price as a Fuel Peat can be compared as a fuel directly to other fuels. The price would reflect the investments to the production facility and the running costs of the operation, but would not take the required investments to utiliza- tion facilities into account. In the case of peat, these may have an impact to the feasibility, since there will be a considerable difference between the cost of oil or gas fired equipment and peat fired equipment. On the other hand, there is little difference in investments to peat fired and wood fired furnaces. Table 1 presents recent prices of peat and peat derived fuels, as obtained from several sources for circumstances generally more favorable then in Alaska. TABLE 1. PRICES OF PEAT BASED FUELS IN 1980 $/Million Btu Milled Peat 1.60 - 2.30 Sod Peat 2.90 - 4.20 Peat Briquettes 4.20 - 5.20 Peat Pellets 3.40 - 4.80 Peat Fuel from Wet Carbonization 2.70 - 4.20 SNG from Peat 3.40 - 5.40 5.2 Cost of Heat Generation from Peat The costs of peat fired space heating depend, whether special facilities are needed or not. Figures in Table 2 are based on the assumption that all equipment is purchased for the purpose, and they include all capital costs. In cases where peat can be substituted for wood in existing stoves and furnaces, the cost of heat would be closer to the fuel cost. -27- TABLE 2. HEAT GENERATION COSTS FROM PEAT IN 1980 $/Million Btu Individual House Heating - Sod peat fired 5.70 - 7.00 - Pellet fired 6.70 - 9.50 - Briquette fired 7.00 - 8.70 Centralized Heating - 1 MW plant, sod peat fired 6.60 - 9.30 - 10 MW plant, milled peat fired 4.00 - 4.70 5.3 Cost of Power Generation from Peat The economics of scale are very steep in power generation, as can be seen in Table 3. It is obvious, that the smallest plants are not yet feasible, unless specific reasons raise the price of competing energy forms. TABLE 3. POWER GENERATION COSTS FROM PEAT IN 1980 $/kWh 250 kW cogenerating steam engine plant, sod peat fired 0.18 - 0.26 1 MW cogenerating steam turbine plant, milled peat fired 0.12 - 0.18 30 MW cogenerating steam turbine plant, milled peat fired 0.03 - 0.07 60 MW cogenerating steam turbine plant, milled peat fired 0.02 - 0.04 Table 4 summarizes the characteristics of the plants presented in Tables 2 and 3. -28- taoLE 4. CHanavTERis1iCS ur PEA RED PLANTS Power Output - - - 250 kWe 1 MWe 30 MWe 60 MWe Thermal Output 25 kWt 1 MWt 10 MWt 2 MWt 8 MWt 60 MWt 120 MWt Form of Thermal Hot water/ Hot water/ Energy Hot water Hot water Hot water LP steam LP steam Hot water Hot water Type of peat Sods, fired Briquettes Sods Milled Sods Milled Milled Milled Boiler design Steel furnace Flame-tube Watertube- Two drum One drum One drum One drum firetube watertube watertube watertube watertube Prime mover - - - Steam engine Steam turbine Steam turbine Steam turbine Main steam 8800 lb/hr 31000 1b/hr 300000 1b/hr 660000 1b/hr parameters 230 psi 570 psi 1650 psi 1650 psi (typical) - - - 660°F 680°F 995°F 995°F Delivery time Weeks 11 months 12 months 12 months 18 months 24 months 30 months Total invest- ment cost $4500 $320000 $2.2 MM $1.5 MM $2.5 MM $35 MM $60 MM -29-