Environmental design considerations for thermochemical biomass energy

Biomass 11 (1986) 255-270

Environmental Design Considerations for Thermochemical Biomass Energy

Michael D. Brown, Eddie G. Baker and Lyle K. Mudge

*Pacific Northwest Laboratory, Richland, Washington 99352, USA

(Received 15 August 1986; accepted 6 November 1986)

A B S T R A C T

This paper discusses design considerations to be employed for control technologies which can minimize environmental damage and maximize operability in thermochemical conversion of biomass. Particulate and tar concentrations from both gasification and combustion technologies are examined. Applicable cleaning technologies and practical implementation of these technologies are discussed.

Key words: Biomass, pollutants, environmental, particulates, tars, gasifier, combustor.

INTRODUCTION

Biomass energy is predicted to contribute over 4% by 1990 to the US energy picture. ~ For biomass energy to meet this prediction will require a conscientious effort to reduce environmental effects.

Particulate and hydrocarbon emissions are an unfortunate byproduct of thermochemical conversion of biomass resources to fuel or power. When carbonaceous materials are gasified or combusted, char, ash, tar, and permanent gases are produced. The relative fractions of these four products will vary and depend primarily on the type of conversion, operating conditions, and the feedstock.

One area at least for gasification systems that has not been studied in detail is gas cleaning, primarily for particulate and tar removal. Particu- lates can cause plugging and erosion of downstream equipment and may also be an environmental problem. Plugging of downstream equipment is

*Operated by the Battelle Memorial Institute for the US Department of Energy under contract DE-AC06-76RLO 1830.

255 Biomass 0144-4565/86/S03.50- © Elsevier Applied Science Publishers Ltd, England, 1986. Printed in Great Britain

256 M. D. Brown, E. G. Baker, L. K. Mudge

the primary problem associated with tars. Once they are separated from the gas, tars may be an environmental hazard and present a disposal problem.

The objective of this paper is to evaluate technology for particulate and tar removal primarily from raw gas from biomass gasifiers. To broaden the base of information available biomass combustion was also considered. Gas cleaning technology, particularly for particulate removal, is very similar. Potential environmental problem areas and gaps in the technology that could impede development of biomass utilization were identified.

This paper is divided into three main areas:

-- Conversion Technologies, -- Cleaning Technologies, - - Design Implementation.

Selection of applicable gas cleanup equipment depends primarily on two factors: the type of conversion technology used, and in the case of gasification, the intended end use of the gas. The type of converter, and to some extent, the feedstock, will determine the concentration of particulates and tars in the gas. The end use will define the particulate and tar concentrations which can be tolerated.

An extensive search produced very little data on gas cleaning systems for biomass gasification, particularly for tar removal. Information on gas cleaning systems for coal gasification and biomass combustion was also studied. This provided a base of information on particulate concentrations and removal but still little on tar removal. This information is imperative for proper design and implementation of applicable gas cleaning devices.

CONVERSION TECHNOLOGIES

Biomass can be thermochemically converted to fuel gases, electricity or heat by either gasification or combustion technologies. Various types of gasifiers and combustors exist today and have widely differing contaminant loadings. This section describes the different conversion technologies and outlines typical contaminant loadings which can be used during process evaluation and design.

G a s i f i c a t i o n

Gasifiers react biomass with hot gases (usually steam, air, and/or oxygen) under reducing conditions to form a combustible fuel or synthesis gas.

Design considerations for thermochemical biomass energy 257

Over the years many different types of gasifiers have been constructed for experimental and commercial use. However, most fall into three distinct categories: fixed bed, fluid bed, and entrained flow, referring to the motion of the solids in the gasifier. Each type of gasifier has different operating characteristics which result in significantly different yields of particulates and tars.

Fixed bed updraft units exhibit a countercurrent flow of fuel and gas. Solid fuel is fed from the top by lock hoppers or feeders. The bed of fuel is supported by a grate at the bottom of the reactor. The fuel moves down through the drying zone~ pyrolysis zone, reduction zone, and combustion zone. Ash and unreacted fuel (char) exit through the grate at the bottom. Reactant gases (air, oxygen, steam) are introduced into the reactor through the grate. The hot gases from the combustion zone provide energy for the endothermic processes in the upper zones and exit at the top of the gasifier saturated with pyrolysis oils and water. Approximately 20-25% of the carbon in wood is recovered as liquid products. The condensed liquids usually are in two phases: an aqueous phase containing highly oxygenated water soluble organics (pyroligneous acids), and a separate tar phase. 2 Because of the low velocity of the gases in the reactor and the filtering effect of the bed, the product gas contains little particulate matter.

Production of pyrolysis oils is largely eliminated in fixed bed downdraft gasifiers. As in updraft units solid fuel is fed from the top. However, air which is used in most downdraft units, is introduced concurrently into the combustion zone through a distributor. Pyrolysis oils and moisture from pyrolysis and drying flow down through the high temperature reduction and combustion zones where oils undergo thermal cracking. The product gases exit near the bottom of the reactor. Ash and char leave through a grate at the bottom of the reactor. Low gas velocities result in low particulate loadings in the same range as updraft. Down- draft gasifiers can exhibit very low tar yields depending on the combustion zone temperature.

Crossdraft gasifiers exhibit many of the operating characteristics of downdraft units. Air or air/steam mixtures are introduced in the side of the gasifier near the bottom. Producer gases are drawn off the opposite side. Tars and oils are drawn through the reduction zone and some cracking to lighter components occurs. Some particulates (mostly ash) are entrained in the product gases.

In a fluid bed gasifier the incoming and evolved gases maintain the reactor bed in a turbulent fluid-like state much like a boiling liquid. The result is an expanded reactor bed of char particles and, in most biomass gasifiers, an inert solid such as sand. Because biomass is less dense and


has less ash and fixed carbon than coal the inert solid is used to maintain proper fluidization (prevent bridging and channeling) and to provide additional heat capacity in the bed.

No distinct zones exist in a fluid bed gasifier. Near isothermal operation is maintained with good fluidization. The product gas contains some tars and oils depending on the bed temperature, and does have a fairly large loading of particulates (ash, char, and bed material). These loadings are easily predicted) Depending on the design, ash and char may be removed from the top of the reactor with the product gases, from the bottom of the reactor, from the top of the bed, or a combination of the three.

In an entrained flow (or transport) gasifier, finely sized fuel particles are entrained in the feed gas (usually oxygen and steam) prior to entry into the reactor. Gasification takes place with the feed particles suspended in the gas phase. The product gas, ash, and char leave the top of the reactor. Limited data indicate particulate and tar loadings similar to or greater than those from fluidized bed units.

Typical particulate and tar loadings in the product gas for each type of gasifier have been compiled 4 and are given in Fig. 1. These exhibit a wide range of concentrations due to differences in operating conditions and feedstocks.

These are actual data (some ranges are sparse) from some ten to twenty operational research or commercial gasifiers and can serve as a

rag/Normal m 3

10 1 O0 1,000 10,000 100,000

I I IK \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \~

Fixed Bed Updraft

Fixed Bed Downdraft

Fixed Bed Cross Flow

Fluid Bed

Entrained Bed

Tar Particulates

Fig. 1. Particulate and tar ]oadings in biomass gasifiers.

Design considerations for thermochemical biomass energy 2 5 9

reliable benchmark for design purposes. Better values are attainable in some cases, however, and these should not be construed as minimums.

Particulate sizes are an important design criteria for various gas cleaning devices. Particulates (or tar droplets) below 1-2~ are difficult to remove using conventional technology. Particle size distributions from various gasifiers are given in Table 1. Data are again quite sparse and these values should be used with caution for design purposes.

TABLE 1 Particle Size Distribution from Various Biomass Gasifiers

Particle size microns Updraft 4 Downdraft 5 Fluid bed 6

250 100 50 30 20 10 5 2 1 0.5

99+ 97 96 95 89 81

74 50 30 18 11

99+ 97 87 38 17 2

Tar compositions are also an important design item. A recently completed study of biomass gasification/pyrolysis condensates at PNL 7 concludes that there is no typical tar composition which can be adequately used to represent all thermally produced biomass tars. The tar composition, as well as the amount, is dependent on the operating conditions, principally a time/temperature thermal severity-type function. The properties of the tar therefore appear to vary on a continuum from 'primary' oxygenated pyrolysis tar collected after a short residence time at low temperatures of around 500°C to highly aromatic, deoxygenated tar which is produced at longer residence time at high temperatures of around 900°C.

Typical components of these two basic types of tars are shown in Table 2. Low temperature oxygenates are much more soluble in an aqueous phase and thus constitute a greater environmental hazard to groundwater. High temperature tars exhibit carcinogenic properties. All tars and oils are generally an operational problem with regard to plugged lines, etc.


TABLE 2 Components of Biomass Tars 7

Major organic components

Low temperature oxygenated tars High temperature deoxygenated tars

2-methyl-2-butanol phenol 2-methoxyphenol 4-methyl-2-methoxyphenol 4-hydroxy-3-methoxybenzaldehyde 2, 6-dimethoxyphenol 3, 5-dimethoxy-4-hydroxygenzaldehyde levoglucosan

naphthalene fluorene phenanthrene flouranthrene acephenthylene benz(a)anthracene

Combust ion

Combustion of biomass is generally applied in thin bed spreader stokers, cell type dutch ovens, and suspension burners. Fluidized bed combustors are also increasingly popular. Each of these burners enjoys advantages and disadvantages under varying fuels and operating conditions. In general there is no one unit clearly superior for all conditions. 8

Dutch ovens and underfeed stokers typically have low particulate levels and are easy to operate, but suffer from poor turndown ratios and response times due to the pile method of operation.

Suspension burners and spreader stokers are much more resilient to changes in demand but require a good quality, uninterrupted fuel supply. These units typically show much higher levels of particulate due to the entrained mode of combustion.

Typical water wall spreader stoker boiler particulate emissions are between 0.25 and 3.0 g ft -3 (500-7200 mg m -3) prior to treatment. 9-11 Condensable hydrocarbon levels are reported to be similar (100-10 000 mg m - 3 ) . 12-14 Typical particulate sizes are very similar to those of fluid bed gasification. Over 99% of the particulate is less than 100/~, with less than 2% smaller than 1/~.15 Other studies found much smaller size distributions, with as much as 42% less than 1 be. ~°

Fluidized bed combustors emit similar amounts. Northern States Power operates a 15 MW combustion unit which emits 0.01 g acf-1 (grains per actual cubic foot) of particulates after a gravel bed filter. Inlet concentration is 1 g acf- i)6

Design considerations for thermochemical biornass energy 261

Sampling methods

Standardized methods for sampling tars and particulate emissions from biomass conversion facilities are not well publicized but are available. 17 Other methods (EPA Method 5) are generally preferred for particulate sampling in US facilities. R. F. Weston 1° presents an excellent compila- tion of accepted methods for all species.

GAS CLEANING TECHNOLOGIES

Combustion and fuel gases derived from biomass systems resemble gases derived from coal with respect to major fuel constituents, but differ with respect to major impurities. Because coals are generally much higher in sulfur and ash, these constituents tend to be higher in coal gas than in biomass gas. The spectrum of trace elements derived from coals may also be different from that derived from biomass fuels. Finally, the detailed chemical makeup of tars and oils derived from coals will differ significantly from those derived from biomass. There has been a vast amount of work done on the problem of cleaning coal derived gases and with proper attention to the differences imposed by gasification/combustion of biomass fuels much of this technology can be applied.

Various gas cleanup systems exist for removal of both particulates and tars from gases produced by biomass energy systems. Often these overlap, particularly when tars are present as liquid droplets.

Figure 2 shows a range of particle and droplet sizes and the type of collection mechanism appropriate for various sizes. Although tars are often present as vapor they are removed from the gas as liquid droplets following condensation. Well-documented data with these systems on biomass gas are limited; however, some actual operating data with biomass are included.

Particulate and tar removal

Solid particulate is generally fly ash or char (partially burned feedstock). The class of separators most widely used for removal of particulates are the centrifugal type units (cyclone). For more rigorous removal electrostatic precipitators, baghouses, and other filtering methods are available. These separators are generally operated above the dewpoint of any tars, oils or water that might be present to avoid any sticky combination of tars and char. Depending on the physical properties of the contaminants this may be from 150 to 500°C.


0.001

¢-

U

#_

E "

E ' ~

c rD . LLI

Particle Diameter, microns

0.01 0.1 1 10 100

Fume ;- , ~ Dust

Large Mist ~ ~ Spr3y

Molecules

~ F i b e r Mist E l i m i n a t o r s . ~ i t .

Electrostatic

Precipitators I ~

1,000 10,000

--1 E E

Gravity Sett l ing

Chambers Centrifugal

4 - it Separators

' I - - - Scrubbers it

Impingement 4

Separators

Fig. 2. Particle size classification and useful collection equipment.

Tar removal lowers the heating value of the gas produced by a biomass gasifier. It may become necessary, however, because of the effect of tars in plugging lines and instrument ports rendering operation of downstream equipment difficult. Tars may be present in two forms. In a fixed updraft gasifier where the gas exit temperature is low, tars will be present primarily as liquid droplets entrained in the gas. In downdraft and fluid bed gasifiers where the product gas is hot, tars may also be present in the vapor form. Typical tar removal methods include cyclones, centrifugal separators and wet scrubbers of various kinds. Only at high temperatures can particulate and tar removal be separated. At temperatures where tars and oils condense to liquids, removal of tars and oils cannot be divorced from the particulate removal problem (all collect together).

The main features of commercial and developing particulate and tar removal systems are summarized in Table 3. Cyclones can operate at the highest temperatures followed by dry electrostatic precipitators (ESPs) and granular bed filters. Baghouses are limited to about 290°C by the fabrics they utilize. Liquid scrubbers are limited by the vapor pressure of the scrubbing liquid, usually water. Filter systems capable of operating at higher temperatures are under development. The effects of operating at

Design considerations for thermochemical biornass energy

TABLE 3 Summary of Gas Cleanup Systems 19

263

Commercial systems Maximum operating Inlet or Typical Collects conditions face pressure condensed

velocity drop tars Operated Projected fi min- i in 1420 °F/PSIG °F/PSIG

Cyclones 1700/high > 2000/high 4000 4-6 Yes Electrostatic 900/15 1700/300 200-300 5-35 Yes

Precipitators Bag Houses 550/15 -- 5-10 15-30 No Granular Bed Filters >900/high > 2 0 0 0 / 3 0 0 + 100 9-12 No Liquid Scrubbers 175/15 -- -- 9-12 Yes Aerodyne Tornado 900/500 1700/500 -- 13 Yes Developing systems Fiber Filters - - 1500/high 100 -- No Porous Metal 800/15 > 1500/high 2-5 - - No Ceramic 3450/15 -- 2-5 - - No Liquid Scrubbers 1400/15 1400/100 -- -- Yes Panel Bed 1000/15 > 2000/high 30-45 -- No Ducon 600/15 > 1500/high 30-90 -- No Pebble Bed 250/15 1500/high 30-100 -- No

pressure are known for cyclones, electrostatic precipitators, barrier filters, and other hot gas cleaning methods. 18 Generally, pressurized operation reduces the size of gas cleaning equipment. Wet scrubbers, however, are generally used only at atmospheric pressure and consequently have not been researched extensively. Research in this area would be beneficial.

Typical efficiencies for several of the most common gas cleaning systems as a function of particle size are shown in Fig. 3. Cyclone separators are the least efficient. Wet scrubbers are somewhat more efficient and baghouses (fabric filters) and ESPs are the most efficient particularly for submicron particles.

END USES FOR BIOMASS GAS

Low-Btu gas (producer gas) from biomass has been used to fire various industrial process burners including direct fired equipment such as dryers and kilns and indirect fired equipment such as boilers and oil heaters. Low-Btu gas has also been used as a fuel for internal combustion reciprocating engines, both gasoline and diesel, and is being considered


99,9,

99

95

.~ 90

.2 80 =: ¢u 70 ~ 6o ~ 5o m~ o 4 0 U 30

20

Fabric ~ /

- E S P , , , . . . . . ..,,,.,~-"v , . ~ , . ~ , , ~ . , • /

.e- ~ .e.

iS" S S S /

S

/ l I . /

° o ~ °

v s s • /

0.1 ~ 0.02 0.1 1 10

Particle Diameter, Microns

Fig. 3, Typical efficiencies for various gas cleaning methods.

for use in gas turbine engines. Medium-Btu gas can be substituted for low-Btu gas in these applications. In addition it can be used as a synthesis gas for making such fuels as methanol, methane (SNG), and liquid hydrocarbon fuels. The amount of gas cleanup required will depend on the intended end use of the gas. This section discusses the gas quality, primarily the tar and particulate levels, that are required for each of these end uses.

The allowable particulate and tar loadings in biomass gas varies significantly depending on the end use. Figure 4 summarizes the requirements for particulates. If the gas is used in a burner to supply energy, particulate removal will be governed primarily by air pollution regulations for particulates. The allowable loadings in the combustion flue gas range from 0.03 to 0"6 lb 10 -6 Btu (approximately 70-1500 mg m -3) depending on the size and location of the facility.

For internal combustion engines, particulates must be removed down to 10-50 mg m -3 to prevent excessive engine wear. Requirements are even more strict to prevent erosion and corrosion of gas turbine blades;


~ looo

1 O0 z_

g

g.

i • 0 0 0 1 1.C- lO/. 1

I . 1 - 1 1 -

0 0 0 0 1

0.1

I 01- 0 1 ! -

0 0 0 0 1 !

0 0 1

• 0 0 ' - 001 - 0 0 0 0 1

(,3 ~0 {,0

O~ 0

1 ~ 0

0

Unacceptab le

Regulat ions

NSPS (Federal )

Acceptab le

Fig. 4. Allowable particulate loadings for various end uses.

particulates must be reduced to 0.001-0.01 g scf-~ (grains per standard cubic foot) (2-20 mg m -3) depending on turbine speed and operating temperature.~8

Less information is available for gases to be used for synthesis of chemicals, SNG, or gasoline. In general the requirements will be similar to specifications for gas turbine applications and will be dictated by erosion of compressor blades in the compressors used to compress the gas to high pressures required for synthesis.

Specifications for tars in the product gas are not well defined. Tars will be consumed in any burner (including gas turbine combustors) and will increase the heating value of the gas. However, this requires close- coupling the gasifier and the burner. Separation of the gasifier and the burner by any distance can cause significant problems due to tar condensation and precipitation. Tar removal should be considered in this case.

In diesel and spark ignition engines tars must be reduced to 10-50 mg m -3 to prevent deposition in the gas mixer and inlet values and gum formation on the valves. The limit on condensable hydrocarbons entering a high temperature gas turbine has been set as low as 0.5 lb 10 -6 scf ( - 8 mg m-3) although no reasons have been given for the limitation.

Tars are known to be poisons for various synthesis catalysts, however, their effect is not well understood, nor have limits been set. For synthetic


natural gas entering a pipeline a hydrocarbon dew point of < 40°F at 1000 psig ( - 1 0 0 mg m -3) has been specified. In addition no gum formers are allowed. Tars would probably be classified as gum formers.

DESIGN IMPLEMENTATION

In practice there are a multitude of equipment combinations available for cleaning gases produced by biomass gasification and combustion. Each type of gasifier has cleanup options which are best suited to that particular gasifier. Calculations of system efficiency and end use applicability consider: pollutant concentrations, gas cleanup devices, and end uses. Based on previous experience and literature data (or lack of it) there are two items essential to the design of trouble free gas cleaning systems: (1), particulates and tar should not be removed in the same step due to the sludge that can result; and (2), when tar removal is necessary, wet scrubbing to condense and remove tars will be required (no other removal techniques are considered applicable to tar removal). This method is used for tar removal in commercial fixed bed coal gasifiers. 2~ While these assumptions may not be strictly true, they represent the current state-of-the-art as we see it.

Particulate removal for biomass combustion systems appears to be compatible with many combinations of cyclones, ESPs, and scrubbers. Baghouses are not used extensively due to the tendency for filter fires.

For fixed bed gasifiers several technologies are not considered applicable because they would remove particulates and tar together. In general, water scrubbing is the only applicable method of scrubbing tars and oils along with char particles. For fluid bed and entrained bed gasifiers wet scrubbers as a first cleanup step are probably not applicable as tar and particulates would both be removed. This would also result in a significant energy penalty for these high-temperature gasifiers.

Table 4 shows the gas cleanup combinations that achieve particulate performance standards for the various end uses. Where tar removal was required it was assumed that wet scrubbing would meet the tar removal requirements.

The results in Table 4 show that, in general, particle scrubbing appears to be adequate to deal with biomass gas if simultaneous removal of tar is not required. However, additional engineering data are necessary to properly design gas cleaning systems to assure that the system operates reliably and that environmental restrictions are met. These include the size and composition of particulates emitted and the effect of gasifier operating variables on emissions.

Design considerations for thermochemical biomass energy

T A B L E 4 Applicable Gas Cleaning Options

267

Performance standards

Close-coupled Diesel or Gas turbine Syn gas or SNG boiler spark-ignition 1-80 mg m -3 1-80 mg m -~

200-1500 mg m - -~ engine 10-50 mg m- ~

Fixed bed updraft ~ None b

Fixed bed downdraft None b C

Fluidized bed 2C h,' C+WS C + F ESPh, a

Entrained bed Similar to fluidized bed

WS + F WS h WS h WS + F WS + F WS + ESP WS + ESP ESP ~ ESP b

Cb.e C h C b C + F 2C b 2C h WS b C + F C + F WS + F C + ES P C + ESP C + F C+WS b C+WS b C+WS ~ C + F C + F C + ESP b,a C + ESP a C + ESP a

f f

C = clycione; 2C = two cyclones in series; F = fabric filter (baghouse); WS = wet scrubber; ESP= electrostatic precipitator.

Cyclone not effective due to smaller particle size distribution and tar droplets -- use wet scrubber to remove tars first if any cleanup is required. b Lower level of contaminants is acceptable -- higher level would exceed limits. ' Assumes 50% of particulate is char and 90% burns in burner. aESP is not as effective on particulates with high carbon content and may not be applicable. ~Cyclones are effective for this application but wet scrubbers are often used instead because gas cooling is also required. Also cyclone efficiency is affected by large turndown ratio required in some engine applications. 1Pressurized operation may restrict the size or applicability of gas cleanup equipment (particularly baghouses and ESPs).

T a r s a n d a q u e o u s so lub le o rgan i c s p r e s e n t a u n i q u e p r o b l e m . In s o m e app l i ca t ions , such as in a boi ler , t hey c a n b e u s e d as a fuel d i rec t ly (no r e m o v a l r equ i red) , b u t o f t en they c o n d e n s e a n d c a u s e p lugg ing p r o b l e m s in t r a n s f e r l ines a n d o t h e r d o w n s t r e a m e q u i p m e n t . T a r s m a y b e p r e s e n t as v a p o r o r as an a e r o s o l (smal l l iquid drop le t s ) . T h e r e is n o bas ic u n d e r s t a n d i n g o f h o w va r i ab l e s s u c h as t e m p e r a t u r e , t a r load ing , ta r c o m p o s i t i o n , a n d ve loc i t y a f fec t t a r depos i t i on .

In a d d i t i o n t h e r e is little i n f o r m a t i o n o n ta r r e m o v a l in the l i te ra ture .

We a s s u m e d tha t we t s c r u b b i n g is e f fec t ive fo r b i o m a s s ta r r e m o v a l , bu t


this has not been confirmed in large scale equipment. There are several disadvantages to wet scrubbing. The sensible heat of the gas is lost as is the heating value of water soluble compounds. Wet scrubbing generates a wastewater stream which may present environmental problems. Separa- tion and recovery of biomass tars from wastewater has not yet been proven on a commercial scale.

CONCLUSIONS AND RECOMMENDATIONS

Particulate removal technology appears adequate to deal with biomass gas, especially when simultaneous tar removal is not required. However, more detailed data on particulate loadings, particle size and particle composition from different type gasifiers and more definite limits for various end uses are needed for engineering design of large-scale commercial gas cleanup systems.

Removal of tar from gas streams presents a problem with aspects not previously encountered. Tars from fixed bed biomass gasifiers are most likely present primarily as very small liquid droplets although no information on particle size was found in the literature. A study of the mechanism of tar formation including the effect of gas velocity, temperature, and wood moisture content on tar loadings and liquid particle diameters would aid significantly not only in gas stream cleanup design but in gasifier design. In conjunction with this, research on the efficiency of various wet scrubbing techniques for tar removal is needed for design of wet scrubbing systems. Tars from downdraft and fluid bed gasifiers are probably present primarily as vapors although this has not been confirmed. Tar removal will require cooling and water scrubbing. The size of droplets formed by quenching and the effect of the method of quenching on the efficiency of tar removal need to be studied. Water scrubbing produces a wastewater stream containing tars and water soluble organics which may present an environmental problem. Research on separation of tars from the aqueous layer and methods of treatment and disposal of the water is needed. Thermal or catalytic cracking of tars to convert them to gas and char should be considered as an alternative to a water scrubber.

Standardized analysis and reporting requirements are desirable for biomass energy facilities so that comparisons can be made on an equal basis. A high quality handbook encompassing all environmental aspects of design for biomass energy is needed.


A C K N O W I . F D G M E N T S

This article was prepared by the Pacific Northwest Laboratory (PNL) for the Biomass Thermochemical Conversion Program of the US Depart- ment of Energy (DOE) under contract number DE-AC06-76RLO- 1830. The guidance and support provided by Gary F. Schiefelbein and Mark A. Gerber of the Program Office and Simon Friedrich of DOE are greatly appreciated.

R E F E R E N C E S

1. Klass, D. L. (1985). Energy from biomass and wastes: 1984 update. In: Pro- ceedings of Energy from Biomass and Wastes IX, 28 January-1 February, 1985, Lake Buena Vista, Florida, Institute of Gas Technology, Chicago, Illinois, USA.

2. Mudge, L. K., Ham, D. G., Weber, S. L. & Mitchell, D. H. (1980). Oxygen/ Steam Gasification of Wood, PNL-3353, Pacific Northwest Laboratory, Richland, Washington. Available from National Technical Information Service (NTIS), Springfield, Virginia, USA.

3. Zenz, F. A. (1982). State-of-the-Art Review and Report on Critical Aspects and Scale-Up Considerations in the Design of Fluidized-Bed Reactors- Final Report on Phase 1, DOE/MC/14141-1158. Available from National Technical Information Service (NTIS), Springfield, Virginia, USA.

4. Brown, M. D., Baker, E. G. & Mudge, L. K. (1986). Evaluation of processes for removal of particulates, tars, and oils from biomass gasifier product gases. In: Proceedings of Energy from Biomass and Wastes X, 7-10 April 1986, Washington, DC, Institute of Gas Technology, Chicago, Illinois, USA.

5. SERI (1979). Generator g a s - The Swedish Experience from 1939-1945. SERI/SP-33-140. Solar Energy Research Institute, Golden, Colorado. Available from National Technical Information Service (NTIS), Springfield, Virginia, USA.

6. Datin, D. L., LePori, W. A. & Parnell, C. B. Jr (1981 ). Cleaning low energy gas produced in a fluidized bed gasifier. In: Proceedings of the 1981 Winter Meeting of the American Society of Agricultural Engineers, 15-18 December, 1981, Paper No. 81-3592, Chicago, Illinois.

7. Elliott, D. C. (1985). Analysis and Comparison of Biomass Pyrolysis/ Gasification Condensates, PNL-5555. Pacific Northwest Laboratories, Richland, Washington. Available from National Technical Information Service (NTIS), Springfield, Virginia, USA.

8. Butch, T., Maples, D. & Dyer, D. (1984). Energy from wood: a survey of industrial use of wood waste. Ener. Progr., 4 (3).

9. NCRR (1974). Incineration: A State of the Art Study, National Center for Resource Recovery, D. C. Heath and Co., Lexington, Massachusetts.

10. Weston, R. F. (1985). Stack Emission Standards for Industrial Wood-Fired

270 M. D. Brown, E. G. Baker, L. K: Mudge

Boilers DOE/OR/21389-T2. Available from National Technical Informa- tion Service (NTIS), Springfield, Virginia, USA.

11, Bump, R. L. (1980). Wood waste as fuel and related air pollution control. In: Energy Generation and Cogeneration From Wood, P-80-26, Forest Products Research Society, Madison, Wisconsin, USA.

12. Junge, D. C. (1980). The combustion characteristics of wood and bark residue fuels. Energy Technology, 7, 1331-9.

13. Junge, D. C. (1984). The environment envelope for the operation of a biomass fueled, 10 megawatt topping cycle power generation facility. In: Proceedings of Energy from Biomass and Wastes VIII, 30 January-3 February, 1984, Lake Buena Vista, Florida, Institute of Gas Technology, Chicago, Illinois, USA.

14. Kitto, W. D. (1980). Environmental considerations in wood fuel utilization. In: Progress in Biomass Conversion, Vol. 2, eds K. V. Sarkanen and D. A. Tillman, Academic Press, New York.

15. Brady, J. D. & Jenkins, H. N. (1980). Wood energy emissions control technologies. In Energy Generation and Cogeneration from Wood, P-80-26, Forest Products Research Society, Madison, Wisconsin, USA.

16. Anon (1982). Wood-burning fluidized bed combustion retrofit at NSP slashes fuel cost by 90%. Electric Light and Power, June 1982.

17. Esplin, G. J., Fung, D. P. C. & Hsu, C. C. (1985). Development of sampling and analytical procedures for biomass gasifiers. Can. J. Chem. Eng., 63, 946-53.

18. Baker, E. G., Brown, M. D., Moore, R. H., Mudge, L. K. & Elliott, D. C. (1985). Engineering Analysis of Biomass Gas Cleaning Technology, PNL- 5534, Pacific Northwest Laboratory, Richland, Washington, USA. Avail- able from National Technical Information Service (NTIS), Springfield, Virginia, USA.

19. Stone and Webster Engineering Corp. (1974). Purification of Hot Fuel Gases from Coal or Heavy Oil, EPRI-243-1. Available from National Technical Information Service (NTIS), Springfield, Virginia, USA.

20. Robson, E L. & Giramonti, A. J. (1974). The environmental impact of coal based advanced power generating systems. Symposium Proceedings Environmental Aspects of Fuel Conversion Technology, EPA-650/2-74-118. Available from National Technical Information Service (NTIS), Springfield, Virginia, USA.

21. Kennedy, D. M., Breitstein, L. &Chen, C. (1979). Control technologies for particulate and tar emissions from coal converters. In: Proceedings Environ- mental Aspects of Fuel Conversion Technology. EPA-600/7-79-217. Research Triangle Institute, Research Triangle Park, North Carolina. Avail- able from National Technical Information Service (NTIS), Springfield, Virginia, USA.

Documents

Environmental design considerations for thermochemical biomass energy