Thermochemical Conversion 3

Report
CONVERSION OF BIOMASS TO BIOFUELS
WSU ChE 481/581 & UI BAE 504
THERMOCHEMICAL CONVERSION SECTION
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]
CREDIT HOURS: 3
MEEETING PLACE: EME B46, TUESDAY AND
THURSDAY 1:25-2:40 AM
OUTLINE OF OUR PREVIOUS LECTURE
A.- TORREFACTION
B.- SLOW PYROLYSIS (CARBONIZATION)
C.- FAST PYROLYSIS
D.- CONCLUSION
OVERVIEW OF THE THERMOCHEMICAL SECTION
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
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.
A.- GASIFICATION (700 -1400 oC)
SYNTHESIS GAS CONVERSION PROCESSES
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
A.- GASIFICATION (700 -1400 oC)
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:
 
the actual biomass  air ratio
the biomass  air ratio for complete combustion

m
m
f
f
/ mo 
/ mo 
st

m o st
mo
Where:
mf: mass of biomass (fuel)
Φ > 1 The mixture is rich (Excess of Biomass)
mo: mass of oxidizer (air)
Φ ≤ 1 The mixture is weak (Excess of air)
St: Stoichiometric conditions
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)
AFR 
1

AFR
st
A.- GASIFICATION (700 -1400 oC)
DISTRIBUTION OF ENERGY AND EXERGY TO THE PREODUCT GAS AND CHAR FOR BIOMASS CONVERSION BY AIR
(BIOMASS AND OXYGEN BROUGHT TO EQUILIBRIUM CONDITIONS)
1/ Φ
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
A.- GASIFICATION (700 -1400 oC)
SYNTHESIS OR
CONVERSION
STEAM OR
OXYGEN
MHV
GAS
METHANOL
ETHERS
DIESEL
FUEL CELLS
GASOLINE
HYDROGEN
BIOMASS
GASIFICATION
AIR
TURBINES
LHV
GAS
OPERATIONAL BIOMASS GASIFIERS
GÜSSING: 2 MWe, STEAM, AUSTRIA
HARBOØRE: 1.3 MWe, AIR, DENMARK
ARBRE: 8 MWe, AIR, UK
ENGINE
BOILER
AMMONIA
ELECTRICITY
HEAT
A.- GASIFICATION (700 -1400 oC)
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.
A.- GASIFICATION (700 -1400 oC)
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.
A.- GASIFICATION (700 -1400 oC)
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.
A.- GASIFICATION (700 -1400 oC)
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.
TRADITIONAL PROCESSES:
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.
Reference: Higman C, van der Burgt M: Gasification. Gulf Professional Publishing, Second Edition, 2008
A.- GASIFICATION (700 -1400 oC)
-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
Winkler
process
PRODUCT GAS CHARACTERISTICS
A.- GASIFICATION (700 -1400 oC)
REACTION ZONES IN A STANDARD UPDRAFT GASIFIER
BIOMASS
DRYING ZONE
PYROLYSIS ZONE
OXYGEN
A.- GASIFICATION (700 -1400 oC)
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.
Source: Higman C, van der Burgt: Gasification, Gulf Professional Publishing, Second Edition, 2008.
A.- GASIFICATION (700 -1400 oC)
SASOL-LURGI DRY BOTTOM GASIFIER
PROCESS FLOWSHEET OF SASOL-LURGI DRY BOTTOM GASIFICATION
Source: Higman C, van der Burgt: Gasification, Gulf Professional Publishing, Second Edition, 2008.
A.- GASIFICATION (700 -1400 oC)
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.
Reference: Higman C, van der Burgt M: Gasification. Gulf Professional Publishing, Second Edition, 2008
A.- GASIFICATION (700 -1400 oC)
BGL GASIFIER
COMPARATIVE PERFORMANCE OF LURGI DRY
BOTTOM AND BGL GASIFIERS
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.
Reference: Higman C, van der Burgt M: Gasification. Gulf Professional Publishing, Second Edition, 2008
A.- GASIFICATION (700 -1400 oC)
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 9501100 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.
Reference: Higman C, van der Burgt M: Gasification. Gulf Professional Publishing, Second Edition, 2008
A.- GASIFICATION (700 -1400 oC)
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
Reference: Higman C, van der Burgt M: Gasification. Gulf Professional Publishing, Second Edition, 2008
A.- GASIFICATION (700 -1400 oC)
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.
WINKLER (HTW) PROCESS
THE FEED SYSTEM COMPRISES A LOCKHOPPER 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.
Reference: Higman C, van der Burgt M: Gasification. Gulf Professional Publishing, Second Edition, 2008
A.- GASIFICATION (700 -1400 oC)
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
Reference: Higman C, van der Burgt M: Gasification. Gulf Professional Publishing, Second Edition, 2008
A.- GASIFICATION (700 -1400 oC)
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 UGAS 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
Reference: Higman C, van der Burgt M: Gasification. Gulf Professional Publishing, Second Edition, 2008
A.- GASIFICATION (700 -1400 oC)
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
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
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 KRUPPKOPPERS (PRENFLO).
Reference: Higman C, van der Burgt M: Gasification. Gulf Professional Publishing, Second Edition, 2008
A.- GASIFICATION (700 -1400 oC)
JUST AS WITH MOVING AND FLUIDIZED BED PROCESSES, THE FIRST ENTRAINEDFLOW SLAGGING GASIFICATION PROCESS OPERATED AT ATMOSPHERIC PRESSURE.
THE ATMOSPHERIC PRESSURE KOPPERS-TOTZEK (KT) PROCESS WAS DEVELOPED IN
THE 1940s.
KOPPERS-TOTZEK (KT) PROCESS
THE KT REACTOR FEATURES SIDEMOUNTED
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.
Reference: Higman C, van der Burgt M: Gasification. Gulf Professional Publishing, Second Edition, 2008
A.- GASIFICATION (700 -1400 oC)
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
Reference: Higman C, van der Burgt M: Gasification. Gulf Professional Publishing, Second Edition, 2008
A.- GASIFICATION (700 -1400 oC)
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.
Reference: Higman C, van der Burgt M: Gasification. Gulf Professional Publishing, Second Edition, 2008
A.- GASIFICATION (700 -1400 oC)
BIO-OIL GASIFICATION
GASIFIER
Wright MM, Brown RC, Boateng AA: Distributed Processing of Biomass to Bio-oil for Subsequent Production of Fischer-Tropsh liquids. Bio-fuels, Bioprod., Bioref 2:229238 (2008)
A.- GASIFICATION (700 -1400 oC)
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.
Reference: Higman C, van der Burgt M: Gasification. Gulf Professional Publishing, Second Edition, 2008
A.- GASIFICATION (700 -1400 oC)
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)
Reference: Higman C, van der Burgt M: Gasification. Gulf Professional Publishing, Second Edition, 2008
A.- GASIFICATION (700 -1400 oC)
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.
Reference: Higman C, van der Burgt M: Gasification. Gulf Professional Publishing, Second Edition, 2008
A.- GASIFICATION (700 -1400 oC)
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
B.- COMBUSTION (OVER 1500 oC)
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 %)
FLUE GAS
BOILER
BIOMASS
ELECTRICITY
SUBSTATION
STORAGE
TURBINE
DRYER
GENERATOR
DRYER
EXHAUST
AIR
BOILER
BLOWDOWN
MAKE-UP WATER
DIRECT-FIRED BIOMASS ELECTRICITY GENERATING SYSTEM
SCHEMATICS.
B.- COMBUSTION (OVER 1500 oC)
USUAL AMOUNT OF EXCESS AIR SUPPLIED TO FUEL-BURNING EQUIPMENT
B.- COMBUSTION (OVER 1500 oC)
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.
B.- COMBUSTION (OVER 1500 oC)
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.
B.- COMBUSTION (OVER 1500 oC)
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)
B.- COMBUSTION (OVER 1500 oC)
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.
B.- COMBUSTION (OVER 1500 oC)
CIRCULATING FLUID BED:
B.- COMBUSTION (OVER 1500 oC)
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.
B.- COMBUSTION (OVER 1500 oC)
STOKER COMBUSTORS
C.- HYDROTHERMAL CONVERSION
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.
CATALYTIC HTC
For decomposition of organic contaminants in
water of gaseous fuel production
BIOMASS
HTC
For production of fuel for combustion
HTC
For production of products suitable for further
upgrading
METHANE RICH GAS
HYDROPHOBIC ORGANIC
FUEL
INTERMEDIATE PRODUCTS
TO BE REFINED
Knezevic D: Hydrothermal Conversion of Biomass. Ph D Thesis, University of Twente, 2009
C.- HYDROTHERMAL CONVERSION
GAS
TYPICAL HTC PROCESS
HEAT
BIOMASS
WATER
SLURRY
ALKALI
SOLUTION
(OPTIONAL)
REDUCING
GAS
(OPTIONAL)
HIGH
PRESSURE
PUMP
HEAT
HEAT
REACTOR
PRESSURE
REDUCING
VALVE
PRODUCT
COOLER
LIQUID /
SOLID
PREHEATER
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).
Knezevic D: Hydrothermal Conversion of Biomass. Ph D Thesis, University of Twente, 2009
C.- HYDROTHERMAL CONVERSION
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.
Knezevic D: Hydrothermal Conversion of Biomass. Ph D Thesis, University of Twente, 2009
C.- HYDROTHERMAL CONVERSION
http://www.enertech.com/technology/efuel.html
C.- HYDROTHERMAL CONVERSION
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.
Knezevic D: Hydrothermal Conversion of Biomass. Ph D Thesis, University of Twente, 2009
C.- HYDROTHERMAL CONVERSION
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
C.- HYDROTHERMAL CONVERSION
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.

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