thermochemical energy conversion

CONVERSION OF BIOMASS TO BIOFUELS

WSU ChE 481/581 & UI BAE 504

LECTURER: MANUEL GARCIA-PEREZ , Ph.D.

Department of Biological Systems Engineering

205 L.J. Smith Hall, Phone number: 509-335-7758

e-mail: [email protected]

Thanks for this presentation that is NOW PUT IN WEB

CREDIT HOURS: 3

THERMOCHEMICAL CONVERSION SECTION

mailto:[email protected]



OUTLINE OF OUR PREVIOUS LECTURE

A.- TORREFACTION

B.- SLOW PYROLYSIS (CARBONIZATION)

C.- FAST PYROLYSIS

D.- CONCLUSION

LECTURE 1

INTRODUCTION TO BIOMASS THERMOCHEMICAL CONVERSION TECHNOLOGIES AND THERMO-CHEMICAL REACTIONS

LECTURE 2

TORREFACTION AND PYROLYSIS (SLOW AND FAST)

LECTURE 3

GASIFICATION, COMBUSTION AND HYDROTHERMAL CONVERSION

LECTURE 4

CHARACTERIZATION AND USES OF PRODUCTS OF THERMOCHEMICAL REACTIONS

OVERVIEW OF THE THERMOCHEMICAL SECTION

LECTURE OUTLINE

A.- GASIFICATION

B.- COMBUSTION

C.- HYDROTHERMAL CONVERSION

A.- GASIFICATION (700 -1400 oC)

THERMOCHEMICAL GASIFICATION IS THE CONVERSION BY PARTIAL OXIDATION AT ELEVATED TEMPERATURES OF A CARBONACEOUS FEEDSTOCK INTO A GASEOUS ENERGY CARRIER CONSISTING OF PERMANENT GASES AND TARS. DEVELOPMENT OF GASIFICATION TECHNOLOGIES DATES BACK TO THE END OF THE 18TH CENTURY WHEN HOT GASES FROM COAL AND COKE FURNACES WERE USED IN BOILER AND LIGHTING APPLICATIONS. GASIFICATION OF COAL IS NOW WELL ESTABLISHED, AND BIOMASS GASIFICATION HAS BENEFITED FROM ACTIVITY IN THIS SECTOR. HOWEVER, THE TWO TECHNOLOGIES ARE NOT DIRECTLY COMPARABLE DUE TO DIFFERENCES BETWEEN THE FEEDSTOCKS (E.G. CHAR REACTIVITY, PROXIMATE COMPOSITION, ASH COMPOSITION, MOISTURE CONTENT, DENSITY).

ALTHOUGH MANY BIOMASS GASIFICATION PROCESSES HAVE BEEN DEVELOPED

COMMERCIALLY, ONLY THE FLUID BED CONFIGURATION ARE BEING CONSIDERED IN APPLICATIONS THAT GENERATE OVER 1 MWe. FLUID BED GASIFIERS ARE AVAILABLE FROM A NUMBER OF MANUFACTURERS IN THERMAL CAPACITIES RANGING FROM 2.5 TO 150 MW FOR OPERATIONS AT ATMOSPHERIC AND ELEVATED PRESSURE.

Spath PL, Dayton DC: Preliminary Screening-Technical and Economic Assessment of Synthesis Gas to Fuels and Chemicals with Emphasis on the Potential for Biomass-Derived Syngas. NREL/tp-510-34929

SYNTHESIS GAS CONVERSION PROCESSES


The equivalent ratio (f) is used to quantify the proximity of a mixture (biomass + air (oxygen) to its combustion stoichiometric conditions. The equivalent ratio is denoted as:

o

sto

stof

of

m

m

mm

mm

combustioncompleteforratioairbiomassthe

ratioairbiomassactualthe

/

/

Where:

mf: mass of biomass (fuel)

mo: mass of oxidizer (air)

St: Stoichiometric conditions

Φ > 1 The mixture is rich (Excess of Biomass)

Φ ≤ 1 The mixture is weak (Excess of air)

PYROLYSIS: Φ infinite

GASIFICATION: Φ between 3 and 5 (1/ Φ between 0.15 and 0.28)

COMBUSTION: Φ 0 to 1

The equivalent ratio is related to the air to fuel ratio (AFR)

stAFR1

AFR


DISTRIBUTION OF ENERGY AND EXERGY TO THE PREODUCT GAS AND CHAR FOR BIOMASS CONVERSION BY AIR (BIOMASS AND OXYGEN BROUGHT TO EQUILIBRIUM CONDITIONS)

DISTRIBUTION OF ENERGY AND EXERGY TO THE PREODUCT GAS AND CHAR FOR BIOMASS CONVERSION BY STEAM (STEAM TEMPERATURE 500 K) (BIOMASS AND STEAM BROUGHT TO EQUILIBRIUM CONDITIONS)

MARK JAN PRINS: THERMODYNAMIC ANALYSIS OF BIOMASS GASIFICATION. INCLUDING TORREFACTION AS A THERMAL PRETREATMENT. VDM VERLAG Dr. MULLER. PhD THESIS UNIVERSITY OF EINDHOVEN , 2005


1/ Φ

BIOMASS GASIFICATION

MHV GAS

LHV GAS

STEAM OR OXYGEN

AIR

SYNTHESIS OR CONVERSION

FUEL CELLS

TURBINES

ENGINE

BOILER

METHANOL

ETHERS

DIESEL

GASOLINE

HYDROGEN

AMMONIA

ELECTRICITY

HEAT OPERATIONAL BIOMASS GASIFIERS

GÜSSING: 2 MWe, STEAM, AUSTRIA

HARBOØRE: 1.3 MWe, AIR, DENMARK

ARBRE: 8 MWe, AIR, UK



1812: FOUNDATION OF THE LONDON GAS, LIGHT AND COKE COMPANY FOR THE PRODUCTION OF TOWN GAS

1900: ELECTRIC BULBS REPLACED GAS AS A SOURCE OF LIGHT.

1920: ONLY GAS OF LOW HEATING VALUE (3.5-6 MJ/m3) COULD BE PRODUCED

1920: CARL VON LINDE COMMERCIALIZED THE CRYOGENIC SEPARATION OF AIR ALLOWING TO DEVELOP OXYGEN BLAST FOR THE PRODUCTION OF SYNTHESIS GAS AND HYDROGEN

1926: FRANZ FISCHER AND HANS TROPSCH DEVELOPED THE FISCHER-TROPSCH PROCESS IN GERMANY.

1920-1940: DEVELOPMENT OF NEW GASIFICATION CONCEPTS: 1926- THE WINKLER FLUID BED PROCESS, 1931- THE LURGI MOVING-BED GASIFICATION PROCESS, 1940- THE KOPPERS-TOTZEK ENTRAINED-FLOW PROCESS.

1920-1960: LITTLE FURTHER TECHNICAL PROGRESS IN THE GASIFICATION OF SOLID FUELS BUT THESE TECHNOLOGIES PLAYED A CRITICAL ROLE IN GERMANY’S WARTIME SYNTHESIS FUEL PROGRAM AND ON THE WIDER BASIS IN THE WORLDWIDE DEVELOPMENT OF THE AMMONIA INDUSTRY.

1950: TEXACO AND SHELL DEVELOPED THE OIL GASIFICATION PROCESS, DECLINE IN IMPORTANCE OF GASIFICATION BECAUSE OF THE LARGE PRODUCTION OF NATURAL GAS AND NAPHTHA.

1970: SASOL USES COAL GASIFICATION AND FISCHER TROPSCH SYNTHESIS AS THE BASIS FOR ITS SYNFUELS COMPLEX.

1970: FIRST OIL CRISIS INVESTMENT IN COAL HYDROGENATION (HYDROGASIFICATION) TO PRODUCE METHANE AND LIQUID FUELS. LACK OF COMMERCIAL SUCCESS DUE TO THE NEED FOR HIGH PRESSURE PROCESSED.


1972- PROTOTYPE GASIFICATION PLANTS TO PRODUCE ELECTRICITY FROM COAL GASIFICATION VIA IGCC HAVE BEEN BUILT AND TESTED (COOL WATER, 1984; LUNEN, 1972, BUGGENUM, 1994; WABASH RIVER, 1995; POLK, 1996; PUERTOLLANO 1998).

1978: KOPPERS AND SHELL JOINED FORCES TO PRODUCE A PRESSURIZED VERSION OF THE KOPPERS-TOTZEK GASIFIER.

1981: REINBRAUM DEVELOPED THE HIGH TEMPERATURE WINKLER FLUIDIZED-BED REACTOR

1984: LURGI DEVELOPED A SLAGGING VERSION OF ITS EXISTING TECHNOLOGY IN PARTNERSHIP WITH BRITISH GAS.

1984: TEXACO EXTENDED ITS OIL GASIFICATION PROCESS TO ACCEPT A SLURRIED COAL FEED.

1984- COAL TO CHEMICALS RECEIVED INCREASED ATTENTION (EASTMAN METHANOL PLANT IN KINSPORT STARTED UP IN 1984; Ube IN JAPAN BEGAN WITH COAL TO AMMONIA).

1990- GASIFICATION OF HEAVY OIL RESIDUES IN REFINERIES. FOUR PLANTS WERE BUILT IN ITALY.

2000s- INCREASING IN ENERGY PRICES IS FUELING A RENAISSANCE OF GASIFICATION TECHNOLOGIES. MANY PLANTS ARE BEING BUILT IN CHINA.


GASIFICATION REACTORS CAN BE GROUPED INTO THREE CATEGORIES:

1.- MOVING-BED GASIFIERS

2.-FLUID-BED GASIFIERS

3.-ENTRAINED-FLOW GASIFIERS

MOVING BED GASIFIERS (SOMETIMES CALLED FIXED-BED GASIFIERS) ARE CHARACTERIZED BY A BED IN WHICH THE CARBONACEOUS MATERIAL MOVES SLOWLY DOWNWARD UNDER GRAVITY AS IT IS GASIFIED BY A BLAST THAT IS GENERALLY BUT NOT ALWAYS, IN COUNTER-CURRENT BLAST TO THE CARBONACEOUS MATERIAL. IN SUCH A COUNTER-CURRENT ARRANGEMENT, THE HOT SYNTHESIS GAS FROM THE GASIFICATION ZONE IS USED TO PREHEAT AND PYROLYSE THE DOWNWARD FLOWING SOLID. WITH THIS PROCESS THE OXYGEN CONSUMPTION IS VERY LOW, BUT PYROLYSIS PRODUCTS ARE PRESENT IN THE PRODUCT SYNTHESIS GAS.

FLUID-BED GASIFIERS OFFER EXTREMELY GOOD MIXING BETWEEN FEED AND OXIDANT, WHICH PROMOTES BOTH HEAT AND MASS TRANSFER. CERTAIN AMOUNT OF ONLY PARTIALLY REACTED FUEL IS INEVITABLY REMOVED WITH THE ASH. THIS PLACES A LIMITATION ON THE CARBON CONVERSION OF FLUID BED PROCESSES. THE OPERATION OF FLUID BED GASIFIERS IS GENERALLY RESTRICTED TO TEMPERATURES BELOW THE SOFTENING POINT OF THE ASH, SINCE ASH SLAGGING WILL DISTURB FLUIDIZATION. SIZING OF THE PARTICLE IS VERY IMPORTANT . THE LOWER TEMPERATURE OPERATION OF FLUID BED PROCESSES MEANS THAT THEY ARE MORE SUITED FOR GASIFYING REACTIVE FEEDSCTOCKS, SUCH AS BIOMASS AND LOW-RANK COAL.

Source: Higman C, van der Burgt: Gasification, Gulf Professional Publishing, Second Edition, 2008.


Reference: Higman C, van der Burgt M: Gasification. Gulf Professional Publishing, Second Edition, 2008

ENTRAINED-FLOW GASIFIERS OPERATE WITH FED AND BLAST IN CO-CURRENT FLOW. THE RESIDENCE TIME OF THESE PROCESSES IS SHORT (A FEW SECONDS). THE FEED IS GROUND TO A SIZE OF 100 mm OR LESS TO PROMOTE MASS TRANSFER AND ALLOW TRANSPORT IN THE GAS. GIVEN THE SHORT RESIDENCE TIME, HIGH TEMPERATURES ARE REQUIRED TO ENSURE A GOOD CONVERSION AND THEREFORE ALL ENTRAINED FLOW GASIFIERS OPERATE IN THE SLAGGING RANGE.

ONE IMPORTANT POINT TO KEEP IN MIND IS THE SIGNIFICANCE OF THE SLAGGING BEHAVIOR OF THE ASH. AT TEMPERATURES ABOVE THE ASH SOFTENING POINT, THE ASH BECOMES STICKY AND WILL AGGLOMERATE, CAUSING BLOCKAGE OF BEDS OR FOULING THE HEAT EXCHANGE EQUIPMENT.

GAS PRODUCER: HUMIDIFIED AIR IS BLOWN UPWARD THROUGH A DEEP BED OF COAL OR COKE. THE AIR REACTS WITH THE COAL, THEREBY PRODUCING A GAS WITH A LOWER HEATING VALUE OF ABOUT 6.5 MJ/m3. WHEN USING LOW RANK FEEDSTOCKS THE CALORIFIC VALUE CAN BE AS LOW AS 3.5 MJ/m3.

WATER GAS: STEAM REACTS IN A BATCH PROCESS WITH RED-HOT COKE TO FORM HYDROGEN AND CARBON MONOXIDE. FIRST THE COAL OR COKE IS HEATED BY BLOWING AIR UPWARD THROUGH THE BED AT 1300 oC. THEN THE AIR IS STOPED AND THE STEAM IS PASSED TO PRODUCE SYNTHESIS GAS. WHEN THE TEMPERATURE DROP TO ABOUT 900 oC THE CYCLE IS REPEATED.

TRADITIONAL PROCESSES:

-PARTIAL OXIDATION TO GIVE A LOW (~ 5 MJ/m3) TO MEDIUM (~ 10 – 15 MJ/m3) HEATING VALUE SYNTHESIS GAS (EQUIVALENT RATIO (f ~ 4) TEMPERATURES (700-1400 oC). BIOMASS MOISTURE : LOWER THAN 15 mass %. PROBLEMS (GAS QUALITY , COST REDUCTION)

GASIFICATION REACTORS


PRODUCT GAS CHARACTERISTICS

Winkler process


REACTION ZONES IN A STANDARD UPDRAFT GASIFIER

PYROLYSIS ZONE

DRYING ZONE

OXYGEN

BIOMASS



MOVING BED PROCESSES

MOVING-BED PROCESSES ARE THE OLDEST PROCESSES.

THE PATENT FOR THE LURGI DRY BOTTOM PROCESS OF “COAL PRESSURE GASIFICATION” AS IT IS KNOWN WAS GRANTED IN 1927. IN 1931 LURGI STARTED TO DEVELOP A PRESSURIZED VERSION OF EXISTING ATMOSPHERIC PRODUCER GAS TECHNOLOGY. THE DEVELOPMENT WAS MADE IN CLOSE COLABORATION WITH THE TECHNICAL UNIVERSITY IN BERLIN UNDER THE DIRECTION OF PROFESSOR RUDOLF DRAWE. THE FIRST COMMERCIAL APPLICATION WAS BUILT IN 1936. FURTHER TECHNICAL DEVELOPMENT HAS BEEN PLACED IN A JOINT VENTURE BETWEEN LURGI AND THE LARGEST OPERATOR OF THIS TECHNOLOGY “SASOL”. TODAY THE TECHNOLOGY IS REFERED AS THE SASOL-LURGI DRY BOTTOM GASIFIER.

THE HEARTH OF THE LURGI PROCESS IS THE REACTOR IN WHICH THE BLAST AND SYNGAS FLOW UPWARD IN COUNTER-CURRENT TO THE SOLID. THE REACTOR VESSEL ITSELF IS A DOUBLE-WALLED PRESSURE VESSEL IN WHICH THE ANNUAL SPACE BETWEEN THE TWO WALLS IS FILLED WITH BOILING WATER. THE STEAM IS GENERATED AT A PRESSURE SIMILAR TO THE GASIFICATION PRESSURE, THUS ALLOWING A THIN INNER WALL , WHICH ENHANCES THE COOLING EFFECT. THE ASH IS RECOVERED VIA A ROTATING GRADE IS PRECOOLED BY INCOMING BLAST (OXYGEN OR STEAM) TO ABOUT 300-400 oC.



SASOL-LURGI DRY BOTTOM GASIFIER

PROCESS FLOWSHEET OF SASOL-LURGI DRY BOTTOM GASIFICATION



BRITISH GAS/LURGI SLAGGING GASIFIER (BGL)

THE BGL SLAGGING GASIFIER IS AN EXTENSION OF THE ORIGINAL LURGI PRESSURE GASIFIER WITH THE ASH DISCHARGE DESIGNED FOR SLAGGING CONDITIONS. AN EXISTING LURGI GASIFIER IN WESTFIELD SCOTLAND WAS MODIFIED FOR SLAGGING OPERATION AND OPERATED FOR SEVERAL YEARS. THE UPPER PORTION OF THE BGL GASIFIER IS IDENTICAL TO THAT OF THE SASOL-LURGI DRY BOTTOM GASIFIER. THE BOTTOM IS COMPLETELY REDESIGNED. THE MOTIVATION FOR THE DEVELOPMENT OF A SLAGGING VERSION OF THE EXISTING LURGI INCLUDED THE DESIRE TO:

1.- INCREASE CO AND H2 YIELDS (AT THE EXPENSE OF CO2 AND CH4) 2.- INCREASE SPECIFIC REACTOR THROUGHPUT 3.- HAVE A REACTOR SUITABLE FOR COALS WITH LOW ASH MELTING POINT 4.- HAVE A REACTOR SUITABLE FOR ACCEPTING FINES 5.- REDUCE THE STEAM CONSUMPTION AND CONSEQUENT GAS CONDENSATE PRODUCTION

THE DECLINE IN INTEREST FOR COAL GASIFICATION IN THE 1980s PREVENTED COMMERCIALIZATION OF THIS TECHNOLOGY. IN THE MID 1990s THE FIRST COMMERCIAL PROJECT WAS REALIZED AT SCHWARZE PUMPE IN GERMANY TO GASIFY A MIXTURE OF LIGNITE AND MUNICIPAL SOLID WASTES.



THE LOWER PORTION OF THE REACTOR INCORPORATES A MOLTEN SLAG BATH. THE MOLTEN SLAG IS DRAINED THROUGH A SLAG TAP INTO THE SLAG QUENCH CHAMBER, WHERE IT IS QUENCHED WITH WATER AND SOLIDIFIED. THE SOLID SLAG IS DISCHARGED THROUGH A SLAG LOCK.

BGL GASIFIER COMPARATIVE PERFORMANCE OF LURGI DRY

BOTTOM AND BGL GASIFIERS



FLUID-BED PROCESSES

THE HISTORY OF DEVELOPMENT OF COAL GASIFICATION AND FLUID-BED TECHNOLOGY HAVE BEEN INTIMATELY LINKED SINCE DEVELOPMENT OF THE WINKLER PROCESS IN THE EARLY 1920s.

IN FLUID-BED GASIFICATION PROCESSES THE BLAST HAS TWO FUNCTIONS: (1) AS A REACTANT AND (2) AS A FLUIDIZING MEDIUM FOR THE BED. SOLUTIONS WHERE ONE VARIABLE HAS TO ACCOMPLISH MORE THAN ONE FUNCTION, WILL TEND TO COMPLICATE OR PLACE LIMITATIONS ON THE OPERATION OF THE GASIFIER.

OPERATING TEMPERATURE: IF THE ASH CONTENT OF THE FUEL START TO SOFTEN THEN THE INDIVIDUAL PARTICLES BEGIN TO AGGLOMERATE. THE LARGER PARTICLES FORMED WILL FALL TO THE BOTTOM OF THE BED AND THEIR REMOVAL POSES A CONSIDERABLE PROBLEM. FLUID BED GASIFIERS ALL OPERATE AT TEMPERATURES BELOW THE SOFTENING POINT OF THE ASH WHICH IS TYPICALLY IN THE RANGE 950-1100 oC FOR COAL AND 800-950 oC FOR BIOMASS.

FEED QUALITY: FLUID-BED GASIFIERS TYPICALLY OPERATE ON LOW RANK COAL SUCH AS LIGNITE, PEAT OR BIOMASS (THESE MATERIALS HAVE HIGHER REACTIVITIES AND CAN BE GASIFIED AT LOWER TEMPERATURES). THESE REACTORS OPERATE WITH GROUND COAL.



CARBON CONVERSION: THERE IS WIDE RANGE OF RESIDENCE TIMES OF THE INDIVIDUAL PARTICLES, THUS REMOVAL OF FULLY REACTED PARTICLES, WHICH CONSIST ONLY OF ASH, WILL INEVITABLY BE ASSOCIATED WITH REMOVAL OF UNREACTED CARBON. MAXIMUM CONVERSION EFFICIENCIES (97 %).

THE WINKLER PROCESS

THE WINLER ATMOSPHERIC FLUID-BED PROCESS WAS THE FIRST CONTINUOUS GASIFICATION PROCESS USING OXYGEN RATHER THAN AIR AS BLAST. THE PROCESS WAS PATENTED IN 1922 AND THE FIRST PLANT BUILT IN 1925. SINCE THEN SOME 70 REACTORS HAVE BEEN NUILT AND BROUGHT INTO COMMERCIAL SERVICE BUT HAS NOW BEEN SHUT DOWN FOR ECONOMIC REASONS. IN MOST SYSTEMS OPERATION TEMPERATURE IS MAINTAINED BELOW THE ASH MELTING POINT (950-1050 oC).

WINKLER ATMOSPHERIC FLUID BED GASIFICATION



THE HIGH-TEMPERATURE WINKLER (HTW) PROCESS

THE NAME “HIGH-TEMPERATURE WINKLER” FOR THE PROCESS DEVELOPED BY RHEINBRAUN IS TO SOME EXTENT A MISNOMER. THE MOST IMPORTANT DEVELOPMENT VIS-À-VIS THE ORIGINAL WINKLER PROCESS IS THE INCREASE OF PRESSURE WHICH HAS NOW BEEN DEMONSTRATED AT 30 bar.

THE FEED SYSTEM COMPRISES A LOCK-HOPPER FOR PRESSURIZED AND A SCREW FEEDER FOR THE TRANSPORT OF COAL FROM THE HIGH-PRESSURE CHARGE BIN INTO THE GASIFIER. THE HTW PROCESS INCLUDES HEAT RECOVERY IN A SYNGAS COOLER IN WHICH THE RAW SYNTHESIS GAS IS COOLED FROM 900 TO ABOUT 300 oC. A CERAMIC CANDLE FILTER IS USED DOWNSTREAM OF THE SYNGAS COOLER FOR PARTICLE REMOVAL.

WINKLER (HTW) PROCESS



CIRCULATING FLUIDIZED BED (CFD) PROCESSES

THE CHARACTERISTICS OF A CIRCULATING FLUIDIZED BED COMBINED MANY ADVANTAGES OF THE STATIONARY FLUIDIZED BED AND THE TRANSPORT REACTOR. THE HIGH SLIP VELOCITIES ENSURE GOOD MIXING OF GAS AND SOLIDS, AND THUS PROMOTE EXCELLENT HEAT AND MASS TRANSFER. SMALL PARTICLES ARE CONVERTED IN ONE PASS, OR ARE ENTRAINED, SEPARATED FROM THE GAS AND RETURNED VIA AN EXTERNAL RECYCLE. ONE ADVANTAGE OF THIS SYSTEM IS THAT THE SIZE AND SHAPE OF THE PARTICLES IS LESS IMPORTANT. THIS TYPE OF GASIFIER IS EMINENTLY SUITABLE FOR THE GASIFICATION OF BIOMASS AND WASTES, OF WHICH THE SIZE, SHAPE, AND HENCE THE FLUIDIZATION CHARACTERISTICS ARE MORE DIFFICULT TO CONTROL.

LURGI CIRCULATING FLUID-BED GASIFIER



AGGLOMERATING FLUID-BED PROCESSES

THE IDEA BEHIND AGGLOMERATING FLUID-BED PROCESSES IS TO HAVE A LOCALIZED AREA OF HIGHER TEMPERATURE WHERE THE ASH REACHES ITS SOFTENING POINT AND CAN BEGING TO FUSE. THE PURPOSE OF THIS CONCEPT IS TO ALLOW A LIMITED AGGLOMERATION OF ASH PARTICLES THAT AS THEY GROW AND BECOME TOO HEAVY TO REMAIN IN THE BED, FALL OUT AT THE BOTTOM. THIS PREFERENTIAL SEPARATION OF LOW-CARBON ASH PARTICLES IS DESIGNED TO PERMIT HIGHER CARBON CONVERSION THAN CONVENTIONAL FLUID-BED PROCESSES. THE BURNERS IN THESE GASIFIERS HAVE TWO FUNCTIONS: INTRODUCING THE FLUIDIZING GAS, AND ALSO CREATING A HOT REGION WHERE THE ASH AGGLOMERATION OCCURS. TWO PROCESSES HAVE BEEN DEVELOPED USING THIS PRINCIPLE: THE KELLOG RUST WESTINGHOUSE (KRW) PROCESS, AND THE U-GAS TECHNOLOGY DEVELOPED BY THE INSTITUTE OF GAS TECHNOLOGY (GTI) (1970). A 1O t/DAY PILOT PLANT OF A MODIFIED VERSION OF THE U-GAS FOR BIOMASS (RENUGAS) WAS BUILD IN 1985.

U-GAS GASIFIER



ENTRAINED-FLOW PROCESSES

THE PRINCIPAL ADVANTAGES ARE THE ABILITY TO HANDLE PRACTICALLY ANY COAL, AND TO PRODUCE A CLEAN, TAR-FREE GAS. THE ASH IS PRODUCED IN THE FORM OF AN INERT SLAG OR FRIT. THIS IS

ACHIEVED WITH THE PENALTY OF A OXYGEN. THESE

REACTORS HAVE BECOME THE PREFFERED GASIFIER FOR HARD COALS. THE FINE COAL PARTICLES REACT WITH THE CONCURRENTLY FLOWING STEAM AND OXYGEN. ALL ENTRAINED GASIFIERS ARE OF THE SLAGGING TYPE WHICH IMPLIES THAT THE OPERATING TEMPERATURE IS ABOVE THE ASH MELTING POINT. THIS ENSURES DESTRUCTION OF TARS AND OILS AND, A HGH CARBON CONVERSION OF OVER 99 %. MOREOVER,

THESE REACTORS PRODUCE THE HIGHEST QUALITY SYNTHESIS GAS WITH LOW METHANE CONTENT. THE TWO BEST KNOWN REACTORS ARE THE TOP-FIRED COAL-WATER SLURRY-FEED GASIFIER (GEE PROCESS) AND THE DRY COAL FEED SIDE FIRED GASIFIER DEVELOPED BY SHELL AND KRUPP-KOPPERS (PRENFLO).

TOP-FIRED COAL-WATER SLURRY FEED SLAGGING ENTRAINED-FLOW GASIFIER

SIDE FIRED DRY COAL FEED SLAGGING ENTRAINED-FLOW GASIFIER

TOP FIRED DRY COAL FEED SLAGGING ENTRAINED FLOW GASIFIER



JUST AS WITH MOVING AND FLUIDIZED BED PROCESSES, THE FIRST ENTRAINED-FLOW SLAGGING GASIFICATION PROCESS OPERATED AT ATMOSPHERIC PRESSURE. THE ATMOSPHERIC PRESSURE KOPPERS-TOTZEK (KT) PROCESS WAS DEVELOPED IN THE 1940s.

THE KT REACTOR FEATURES SIDE-MOUNTED BURNER FOR THE INTRODUCTION OF COAL AND OXYGEN, A TOP GAS OUTLET AND A BOTTOM OUTLET FOR THE SLAG. THE GAS LEAVING THE TOP OF THE GASIFIER AT ABOUT 1500 oC IS QUENCHED WITH WATER NEAR THE TOP OF THE REACTOR TO A TEMPERATURE OF ABOUT 900 oC TO RENDER THE SLAG NON-STICKY BEFORE IT ENTERS A WATER TUBE SYNGAS COOLER FOR THE PRODUCTION OF STEAM.

KOPPERS-TOTZEK (KT) PROCESS



SHELL COAL GASIFICATION PROCESS (SCGP)

SHELL AND KOPPERS JOINTLY DEVELOPED A PRESSURIZED VERSION OF THE KOPPERS-TOTZEK PROCESS. IN 1978 THEY STARTED TO OPERATE A 150 t/DAY GASIFIER IN HARBURG, GERMANY. FOR SHELL THE MAIN INTEREST AT THE TIME WAS THE PRODUCTION OF SYNTHETIC FUELS FROM COAL VIA FISCHER-TROPSCH SYNTHESIS. THE SCGP PROCESS FEATURE AN EVEN AMOUNT OF DIAMETRICALLY OPPOSED BURNERS IN THE SIDE-WALL AT THE BOTTOM OF THE REACTOR. COAL IS GROUND IN A MILLING AND DRYING UNIT TO A SIZE OF 90 % BELOW 90 mm, PRESSURIZED IN LOCK-HOPPERS, TRANSPORTED AS A DENSE PHASE AND MIXED NEAR THE OUTLET OF THE BURNER WITH A MIXTURE OF OXYGEN AND STEAM. THE REACTIONS ARE VERY FAST, AND AFTER A RESIDENCE TIME OF 0.5-4 SECONDS THE PRODUCT GAS LEAVES THE REACTOR AT THE TOP AND THE SLAG LEAVES THROUGH AN OPENING IN THE BOTTOM OF THE REACTOR WHERE IT IS QUENCHED IN A WATER BATH. THE TEMPERATURE IS TYPICALLY 1500 oC AND THE PRESSURE 30 - 40 bars.

SHELL COAL GASIFICATION PROCESS



THE SIEMENS SFG PROCESS

THE SIEMENS SFG PROCESS WAS FIRST DEVELOPED IN 1975 FOR THE

GASIFICATION OF LOCAL BROWN COALS. THE FIRST GSP GASIFIER WAS BUILT IN 1984 AT SCHWARZE PUMPE, GERMANY. THE SFG PROCESS FEATUIRES A TOP-FIRED REACTOR, WHERE THE REACTANTS ARE INTRODUCED THORUGH A CENTRALLY MOUNTED BURNER. THIS USE OF A SINGLE BURNER REDUCES THE NUMBER OF FLOWS TO BE CONTROLLED TO THREE (COAL, OXYGEN AND STEAM). THE SLANG AND HOT GAS LEAVE THE GASIFICATION SECTION TOGETHER WHICH REDUCES ANY POTENTIAL FOR BLOCKAGES IN THE SLAG TAP. THE FIGURE SHOWS A REACTOR WITH A SPIRALLY-WOUND COOLING SCREEN, TYPICALLY USED FOR ASH CONTAINING CONVENTIONAL FUELS AND LIQUIDS.

BIO-OIL GASIFICATION

Wright MM, Brown RC, Boateng AA: Distributed Processing of Biomass to Bio-oil for Subsequent Production of Fischer-Tropsh liquids. Bio-fuels, Bioprod., Bioref 2:229-238 (2008)

GASIFIER




WHEN LOOKING AT BIOMASS GASIFICATION IT IS INSTRUCTIVE TO LOOK AT COAL CONVERSION, AS THERE ARE MANY SIMILARITIES. BIOMASS CAN BE CONSIDERED AS A VERY YOUNG COAL. THE TEMPERTURE REQUIERED TO COMPLETE THERMAL GASIFICATION OF BIOMASS IS AROUND 800 - 900 oC.

ON THE OTHER HAND, THERE ARE A NUMBER OF SIGNIFICANT DIFFERENCES BETWEEN

COAL GASIFICATION AND BIOMASS GASIFICATION. THE BIOMASS ASH HAS A COMPARATIVELY LOW MELTING POINT, IN THE MOLTEN STATE IS VERY AGGRESSIVE. BIOMASS IS GENERALLY HIGHLY REACTIVE. BIOMASS IS FIBROUS AND

AT LOW TEMPERATURE IT PRODUCES A LOT OF TARS.

ENTRAINED-FLOW PROCESSES MIGHT HAVE AN APPARENT ATTRACTION IN BEING ABLE TO GENERATE A CLEAN, TAR-FREE GAS, HOWEVER THE AGGRESSIVE CHARACTER OF MOLTEN SLAG SPEAKS AGAINST USING A REFRACTORY. THESE REACTORS REQUIERE VERY SMALL PARTICLE SIZES THAT ARE DIFFICULT TO OBTAIN WITH BIOMASS.

MOVING BED PROCESSES HAVE BEEN APPLIED TO LUMP WOOD, BUT THEY ARE LIMITED TO THIS MATERIAL. FURTHERMORE, IN A COUNTER-FLOW GASIFIER, THE GAS WOULD BE HEAVILY LOADED WITH TAR. THE ALTERNATIVE OF CO-CURRENT FLOW COULD REDUCE THE TAR PROBLEM SUBSTANTIALLY, BUT THE NECESSITY TO MAINTAIN GOOD CONTROL OVER THE BLAST DISTRIBUTION RESTRICT THIS SOLUTION TO VERY SMALL SIZES.



FLUIDIZED BEDS ARE THE MOST COMMONLY USED REACTORS TO GASIFY BIOMASS, MOST OF THE SYSTEMS TRY TO FIND A SOLUTION TO TAR PROBLEMS OUTSIDE THE GASIFIER.

FLOW DIAGRAM OF THE VARNOMO IGCC SYSTEM (20 BARS) (SWEDEN)

CARBONA PRESSURIZED FLUIDIZED BED PROCESS (1996, U-GASIFIER, 30

BARS, DEVELOPED BY GTI) (COMMERCIAL PLANT STARTED IN

DENMARK, IN 2007)

SILVAGAS (BATELLE)



CHOREN PROCESS

DESPITE THE GENERAL TREND OF USING FLUID-BED REACTORS FOR BIOMASS GASIFICATION, CHOREN IS ONE EXAMPLE OF AN ENTRAINED-FLOW GASIFICATION OF BIOMASS. CHOREN ADDRESSES THE TAR ISSUE OF BIOMASS GASIFICATION BY USING A THREE STAGE PROCESS. IN THE FIRST STAGE THE BIOMASS IS PYROLYSED IN THE PRESENCE OF OXYGEN AT TEMPERATURES BETWEEN 400 AND 500 oC. THE PYROLYSIS GAS AND CHAR ARE EXTRACTED SEPARATELY. THE PYROLYSIS GAS IS SUBJECTED TO HIGH TEMPERATURE GASIFICATION IN THE SECOND STAGE AT 1400 oC. THE CHAR IS GASIFIED IN THE THIRD STAGE.

PRODUCTION OF ELECTRICITY

HIGH PRESSURE BIOMASS GASIFICATION COMBINED CYCLE

LOW PRESSURE BIOMASS GASIFICATION COMBINED CYCLE

Craig K.R., Mann M.K. Cost and Performance Analysis of Biomass-Based Integrated Gasification Combined-Cycle (BIGCC) Power Systems. NREL/TP-430-21657


COMBUSTION IS A CHEMICAL REACTION BETWEEN FUEL AND OXIDIZER INVOLVING SIGNIFICANT RELEASE OF ENERGY AS HEAT.

COMPLETE OXIDATION OF BIOMASS TO CO2 AND H2O WITH PRODUCTION OF HEAT (EQUIVALENT RATIO (f

smaller than 1), TEMPERATURES (OVER 1,500 oC)

COMMERCIALLY AVAILABLE, EMISSIONS PROBLEMS, LOW EFFICIENCY AT SMALL SCALE (η ≤ 30 %)

DIRECT-FIRED BIOMASS ELECTRICITY GENERATING SYSTEM SCHEMATICS.

BIOMASS STORAGE

DRYER

DRYER EXHAUST

FLUE GAS

BOILER

TURBINE

GENERATOR

AIR

BOILER BLOWDOWN

MAKE-UP WATER

SUBSTATION ELECTRICITY

B.- COMBUSTION (OVER 1500 oC)

USUAL AMOUNT OF EXCESS AIR SUPPLIED TO FUEL-BURNING EQUIPMENT



THE COMBUSTION OF SOLID BIOMASS IS FULLY ESTABLISHED AND ALREADY WIDELY USED IN BIOMASS APPLICATIONS. THE COMBUSTION PROPERTIES OF BIOMASS ARE WELL UNDERSTOOD. THE MOST POPULAR COMBUSTORS FOR BIOMASS APPLICATIONS

ARE EITHER STOKER-FIRED AND FLUID BED DESIGNS, ALTHOUGH IN RECENT YEARS THE OPTION TO CO-FIRE SMALL PROPORTIONS OF BIOMASS WITH COAL IN LARGE SUSPENSION FIRED FURNACES HAS ATTRACTED WIDESPREAD INTEREST.

IN STROKER-FIRED COMBUSTORS THE FEED BURNS AS IT MOVES THROUGH THE

FURNACE WHILE RESTING ON A STATIONARY OR MOVING GRATE.

FLUID BED DESIGNS BURN THE FEED IN A TURBULENT BED OF INERT MATERIAL THAT IS FLUIDIZED BY COMBUSTION AIR FLOWING THROUGH IT FROM UNDERNEATH. ALTHOUGH THE GRATE-FIRED COMBUSTORS ARE THE NORM FOR OLDER BIOMASS

FIRED PLANTS, FLUID BED COMBUSTORS ARE RAPIDLY BECOMING THE PREFERRED TECHNOLOGY FOR BIOMASS COMBUSTION BECAUSE OF THEIR LOW NOX EMISSIONS. FLUIDIZED BED BOILERS HAVE BEEN COMMERCIALLY AVAILABLE FOR OVER 20 YEARS, AT CAPACITIES RANGING FROM 15 TO 715 MW INPUT. BUBBLING FLUID BED TEND TO BE LIMITED TO THE LOWER SIZE RANGE, WHILE CIRCULATING FLUID BEDS ARE REPORTED OVER THE ENTIRE CAPACITY RANGE. OVER 110 FLUID BEDS ARE OPERATING IN U.S. ALL WITH PERFORMANCE GUARANTEES FROM THE VENDOR.

DIRECT COMBUSTION SYSTEMS: DIRECT COMBUSTION SYSTEMS COMMONLY USED FOR COMBUSTION OF BIOMASS FUELS CAN BE CLASSIFIED INTO PILE, SUSPENSION, AND FLUIDIZED BED COMBUSTION SYSTEMS.

PILE COMBUSTION SYSTEMS BURN THE WOOD FUEL IN EITHER A HEAPED PILE SUPPORTED ON A GRATE (USED FOR SMALLER SCALE SYSTEMS) WHICH ARE HORIZONTAL OR INCLINED, OR IN A THINLY SPREAD PILE SPREAD ACROSS A GRATE WHICH MAY BE TRAVELING OR STATIONARY. COMBUSTION AIR IS PROVIDED BOTH UNDER THE GRATE AND ABOVE THE FUEL PILE. THE MAIN ADVANTAGES OF THESE BURNERS ARE: RELATIVELY SIMPLE TO DESIGN, LOW CAPITAL AND OPERATING COSTS, ABILITY TO TAKE A FAIRLY WIDE RANGE OF WOOD PARTICLES AND MOISTURE CONTENTS. MOISTURE CONTENTS UP TO 65 % CAN BE BURNED. MINIMUM PARTICLE SIZE DEPENDS ON THE GRATE OPENINGS WHILE THE MAXIMUM PARTICLE SIZE DEPENDS ON THE FUEL FEED OPENING INTO THE COMBUSTION CHAMBER.

SUSPENSION COMBUSTION SYSTEMS ARE OF TWO TYPES, WITH BOTH REQUIRING FUEL MOISTURE LESS THAN 15 PERCENT AND UNIFORM PARTICLE SIZES WITH MAXIMUM DIMENSIONS LESS THAN 6 mm. SUSPENSION BURNERS INCLUDE CYCLONIC BURNERS AND PNEUMATIC SPREADER-STOKER SYSTEMS THAT BURN FUEL PARTICLES SUSPENDED IN A TUBULAR AIR STREAM. CYCLONIC BURNERS CONSIST OF HORIZONTAL OR VERTICAL CYLINDERS OF CYCLONES WITH WOOD PNEUMATICALLY INJECTED ALONG THE TANGENT OF THE BURN CHAMBER. CENTRAL FORCE SUSPENDS THE PARTICLES WHILE THEY ARE BURNED.



FLUIDIZED BED COMBUSTION (FBC) SYSTEMS BURN THE WOOD FUEL ON A HIGH TEMPERATURE BED OF FINELY DIVIDED INERT MATERIAL, SUCH AS SAND, THAT IS AGITATED BY AIR BLOWN FROM BENEATH THE BED. SOLID FUEL IS INTRODUCED INTO THE CHAMBER VIA AN AIRLOCK, WHERE THE FUEL PARTICLE, WHERE THE FUEL PARTICLE BURN WHILE SUSPENDED IN THE BED. A STREAM OF GASES PASSES UPWARDS THROUGH A BED OF FREE FLOWING GRANULAR MATERIALS IN WHICH THE GAS VELOCITY IS LARGE ENOUGH THAT THE SOLID PARTICLES ARE WIDELY SEPERATED AND CIRCULATED FREELY THORUGHOUT THE BED. DURING OVERALL CIRCULATION OF THE BED THERE WILL BE TRANSIENT STREAMS OF GAS FLOWING UPWARDS IN CHANNELS CONTAINING FEW SOLIDS AND CLUMPS OR MASSES OF SOLIDS FLOWING DOWNWARDS. THE FLUIDIZED BED LOOKS LIKE A BOILING LIQUID. THE BED IS USUALLY SAND OR LIMESTINE. OVERFIRE IS NORMALLY INTRODUCED IN THE DISENGAGING ZONE ( FREEBOARD)


CIRCULATING FLUID BED: IF THE AIR FLOW OF A BUBBLING FLUID BED IS INCREASED, THE AIR BUBBLES BECOME LARGER FORMING LARGE VOIDS IN THE BED AND ENTRAINING SUBSTANTIAL AMOUNTS OF SOLIDS. THIS TYPE OF BED IS REFERRED TO AS TURBULENT FLUID BED. IN A CIRCULATING FLUID BED THE TURBULENT BED SOLIDS ARE COLLECTED, SEPARATED FROM THE GAS AND RETURNED TO THE BED, FORMING A SOLID CIRCULATION LOOP. A CIRCULATING FLUID BED CAN BE DIFFERENTIATED FROM A BUBBLING FLUID BED IN THAT THERE IS NO DISTINCT SEPARATION BETWEEN THE DENSE SOLID ZONE AND THE DILUTED SOLIDS ZONE. CIRCULATING FLUID BED DENSITIES ARE ABOUT 560 Kg/M3 COMPARED TO A BUBBLING BED DENSITY OF 720 Kg/M3 . TO ACHIEVE THE LOWER BED DENSITY AIR RATES ARE INCREASED FROM THE 1.5 – 3.7 m/s OF BUBLING BED TO ABOUT 9.1 m/s. THE RESIDENCE TIME OF THE SOLIDS IN A CIRCULATING FLUID BED IS DETERMINED BY THE SOLIDS CIRCULATION RATE, THE ATTRITIBILITY OF THE SOLIDS, AND THE COLLECTION EFFICIENCY OF THE SOLIDS SEPARATION DEVICE.


CIRCULATING FLUID BED:


STOKER COMBUSTORS IMPROVE ON OPERATION OF THE PILE BURNERS BY PROVIDING A MOVING GRATE WHICH PERMITS CONTINUOUS ASH COLLECTION, THIS ELIMINATING CYCLIC OPERATION CHARACTERISTIC OF TRADITIONAL PILE BURNERS. IN ADDITION, THE FUEL IS SPREAD MORE EVENLY, NORMALLY BY PNEUMATIC STOKER AND IN THINNER LAYER IN THE COMBUSTION ZONE FIVING MORE EFFICIENT COMBUSTION. (STOKER FIRED BOILERS WERE FIRST INTRODUCED IN THE 1920s FOR COAL AND IN THE LATE 1940s THE DETROIT STOKER INSTALLED THE FIRST TRAVELLING GRATE SPREADER STOKER FOR WOOD. IN THE BASIC STOKER DESIGN THE BOTTOM OF THE FURNACE IS A MOVING GRATE WHICH IS COOLED BY UNDERFIRE AIR. UNDERFIRE AIR DEFINES THE MAXIMUM TEMPERATURE OF THE GRATE AND THUS THE ALLOWABLE MOISTURE CONTENT OF THE FEED. STAGED COMBUSTION PROCESSES WERE DEVELOPED IN THE 1980’S TO MEET THE TIGHTER NOX EMISSION LIMITS. FOR 40 % EXCESS AIR THE OVERFIRE AIR GAS BEEN INCREASED TO 50 %, LOWERING THE MAXIMUM TEMPERATURE IN THE FURNACE.


STOKER COMBUSTORS


HYDROTHERMAL CONVERSION (HTC) IS A THERMO-CHEMICAL CONVERSION TECHNIQUE WHICH USES LIQUID SUB-CRITICAL WATER AS AREACTION MEDIUM FOR CONVERSION OF WET BIOMASS AND WASTE STREAMS.

HYDROTHERMAL CONVERSION (HTC) CAN BE PERFORMED WITH VARIOUS PURPOSES AND DIFFERENT PRODUCTS CAN BE AIMED FOR. IN A CATALYTIC VERSION OF THE PROCESS ALMOST COMPLETE CONVERSION OF BIOMASS TO METHANE IS REALIZED.

BIOMASS

METHANE RICH GAS

HYDROPHOBIC ORGANIC FUEL

INTERMEDIATE PRODUCTS TO BE REFINED

For decomposition of organic contaminants in water of gaseous fuel production

CATALYTIC HTC

HTC

For production of fuel for combustion

HTC

For production of products suitable for further upgrading

Knezevic D: Hydrothermal Conversion of Biomass. Ph D Thesis, University of Twente, 2009


TYPICAL HTC PROCESS

BIOMASS WATER SLURRY

ALKALI SOLUTION

(OPTIONAL)

REDUCING GAS

(OPTIONAL)

HIGH PRESSURE

PUMP

PREHEATER

REA

CTO

R

GAS

LIQUID / SOLID

PRODUCT COOLER

PRESSURE REDUCING

VALVE

HEAT

HEAT

HEAT


PRIOR TO FEEDING INTO THE PROCESS BIOMASS IS PRETREATED TO ENSURE THAT THE FEEDSTOCK HAS DESIRED PROPERTIES: RHEOLOGICAL PROPERTIES, WATER CONTENT. IN THE FEEDING SECTION, FEEDSTOCK IS PRESSURIZED AND HEATED TO THE DESIRED TEMPERATURE (300-370 oC). FEEDING BIOMASS-WATER SURRIES IS A PARTICULAR CHALLENGE DUE TO THE PROBLEMS OF BIOMASS SETTLING AND BLOCKING THE PROCESS LINES. IN MOST CASES TUBULAR REACTORS HAVE BEEN USED FOR CONTINUOUS INSTALLATIONS. TYPICALLY RESIDENCE TIMES OF 5-90 MINUTES ARE APPLIED. UPON COOLING THREE DIFFERENT PRODUCTS ARE OBTAINED: HYDROPHOBIC ORGANIC PHASE, AND AQUEOUS PHASE WITH ORGANIC COMPOUNDS DISOLVED AND GASES (MAINLY CO2).


1970’s: INTEREST IN ALTERNATIVE ENERGY SOURCES INCREASES DUE TO THE OIL CRISES.

1971: THE US BUREAU OF MINES STUDIED THE CONVERSION OF CARBOHYDRATES IN HOT COMPRESSED WATER IN THE PRESENCE OF CO AND Na2CO3. DEVELOPMENT OF A 18 kg /h WOOD PROCESS DEVELOPMENT UNIT IN ALBANY.

1980’s: HTC USING BIOMASS/WATER SLURRIES WITH SPECIAL FEEDING SYSTEMS WAS STUDIED AT THE UNIVERSITY OF ARIZONA, THE UNIVERSITY OF SASKATCHEWAN, PNNL AND SHELL.

1990’s AFTER A PERIOD OF REDUCED ATTENTION, THE INTEREST IN CONVERSION OF BIOMASS INTO ENERGY WAS RENEWED IN THE MID 1990’s. THE HYDRO-THERMAL UPGRADING (HTU) PROGRAM OF SHELL WAS RESTARTED AT BENCH AND LABORATORY SCALE.

2000’s THE FIVE TONS PER DAY STORS PROCESS DEMONSTRATION PLANT WAS BUILD IN JAPAN WITH THE AIM OF CONVERTING SEWAGE INTO A COMBUSTIBLE ENERGY CARRIER. AFTER THE SUCCESS OF THE PLANT TREATING MUNICIPAL WASTEWATER IN COLTON, CALIFORNIA, THE PROCESS IS NOW COMMERCIALIZED BY THERMOENERGY (US) UNDER THE NAME: THERMOFUEL PROCESS. ENERTECH ENVIRONMENTAL INC (US) IS CURRENTLY BUILDING A COMMERCIAL SCALE FACILITY IN RIALTO, CALIFORNIA TO PROCESS 170 tons/day OF BIO-SOLIDS FROM FIVE MUNICIPALITIES IN LOS ANGELES AREA (IT IS BEING COMMERCIALIZED WITH THE NAME SLURRYCARB).

HYDROTHERMAL CONVERSION OF SPECIFIC FEEDSTOCK TO HYDROPHOBIC FUELS FOR COMBUSTION IS NEARING COMMERCIAL OPERATION. HTC FOR BROADER RANGE OF FEEDSTOCKS AND FOR PRODUCTION OF PRECURSORS OF TRANSPORTATION FUELS IS STILL IN THE DEVELOPMENT STAGE.



http://www.enertech.com/technology/efuel.html


HTC REACTION CHEMISTRY

HTC REACTIONS CAN BE CLASSIFIED ACCORDING TO THEIR MECHANISM AS: IONIC AND FREE RADICAL REACTIONS.

HYDROLYSIS: IS A CLASS OF DECOMPOSITION REACTIONS OF ORGANICS INVOLVING BREAKDOWN BY WATER. THIS IS A TYPICAL IONIC REACTION CATALYZED WITH BASES AND ACIDS. THESE REACTIONS READILY OCCUR ALREADY IN THE TEMPERATURE RANGE OF 150 TO 250 oC WHEN AUTOCATALYSIS IS CAUSED BY ACIDIC HTC REACTION PRODUCTS.

HEMICELLULOSE UNDERGOES HYDROLYSIS DECOMPOSITION AT TEMPERATURES FROM 120 TO 180 oC; HYDROLYSIS OF CELLULOSE OCCURS AT TEMPERATURES ABOVE 180 oC. AT THESE TEMPERATURES IT IS ONLY POSSIBLE TO OBTAIN A PARTIAL HYDROLYSIS OF LIGNIN. COMPLETE DISSOLUTION OF WHOLE BIOMASS CAN BE ACHIEVED WITH Na2CO3.

OXYGEN REMOVAL UNDER THE HTC CONDITIONS OCCURS VIA THE FOLLOWING REACTIONS : DEHYDRATION, DECARBOXYLATION AND DECARBONYLATION. FURTHERMORE WATER IS THE PRODUCT OF POLYCONDENSATION REACTIONS WHICH ARE ONE OF THE MAIN ROUTES TOWARDS CHAR.


CELLULOSE DECOMPOSITION IN SUPERCRITICAL WATER (SAKA MODEL)

Ehara K, Saka S: A comparative study on chemical conversion of cellulose between the batch-type and flow-type systems in supercritical water. Cellulose 9: 301-311, 2002



ROLE OF WATER

WATER UNDER THE HTC HAS SEVERAL ROLES. IT IS A REACTION MEDIUM AND CAN SERVE AS A DISTRIBUTION MEDIUM FOR HOMOGENEOUS AND HETEROGENEOUS CATALYSTS . MOREOVER, WATER ITSELF HAS A CATALYTIC ROLE IN VARIOUS ACID/BASE CATALYZED PROCESSES DUE TO ITS HIGHER DEGREE OF IONIZATION AT THE INCREASED TEMPERATURE. WATER IS ALSO DIRECTLY INVOLVED IN CHEMICAL REACTIONS AS A REACTANT OR A PRODUCT. WATER PARTICIPATES IN THE HYDROLYSIS OF CELLULOSE, IT CAN ALSO OXIDIZE SOME ORGANIC SPECIES . IT IS A POWERFUL POLAR ORGANIC SOLVENT THAT CAN REMOVE THE REACTION INTERMEDIARIES FROM THE SOLID MATRIX AND SERVE AS A PHYSICAL BARRIER BETWEEN THEM TO REDUCE POLYCONDENSATION REACTIONS.

D.- CONLCUSIONS

TORREFACTION, CARBONIZATION, FAST PYROLYSIS, GASIFICATION, COMBUSTION AND HYDROTHERMAL CONVERSION ARE IMPORTANT THERMOCHEMICAL TECHNOLOGIES TO CONVERT LIGNOCELLULOSIC MATERIALS INTO HEAT, PRECURSORS OF TRANSPORTATION FUELS OR CHEMICALS. COMBUSTION IS THE ONLY OF THESE TECHNOLOGIES IN COMMERCIALIZATION THE OTHERS ARE STILL AT THE DEMONSTRATION STAGE.