Hauserman Associates, Inc.
Engineering / Consulting      bill@hauserman-engineering.com

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Specialty:  GASIFICATION

 

ABOUT PYROLYSIS AND GASIFICATION

(An area of specialized experience offered) 

 Any solid or liquid carbonaceous material can be simply and cleanly converted to a clean low-energy fuel gas or – a bit les simply -  gasoline, diesel, methane, alcohols or other chemicals. Massive supplies of feed materials for proven processes are available and under-utilized:

  • Coal

  • Municipal garbage

  • Specific  waste materials

  • Heavy, off-spec or waste crude oil.

  • “Energy crop” wood and other biomass.

  • Agricultural residues (Corn stalks, Bagasse, forest waste.)


BASIC CHEMISTRY

Pyrolysis  happens when any carbonaceous material  is heated to 700ºC to 1000ºC or higher, without burning it.  This is the first thing to happen as the material is heated.

(1)     Feed + Heat   -->    Char  (Near-pure carbon)

          +  Condensables (Tars & Oils) + Gasses (Mostly H2, CO, CO2, CH4)

Gasification  happens  when Char is combined with steam at high temperatures.

(2)    C  +  H2O  +  Heat    -->    H2  +  CO

Concurrent Reactions, happening to a lesser extent, depending on temperature, pressure and  proportion or reactants present. 

(3)     CO  +  H2  -->    H2  +  CO2  +  Heat

(4)     CO  +  3 H2    -->    CH4  +  H2O  +  Heat

Since the  heat released by Reactions (3) and (4) is never enough to sustain (1) and (2),  more heat must be supplied either indirectly (from outside)  or by –

Combustion

(5)    C  +  O2     --->    CO2  +  Heat

(6)     C  +  ½ O2   --->   CO    +   Heat

Combustion of part of the feed is by far the most usual means of providing enough heat to sustain the highly endothermic Pyrolysis and Gasification reactions.  A major process design objective is to minimize combustion, in order to –

  • Minimize the amount of feed consumed by combustion.

  • Maximize Overall Thermal Efficiency.

  • Reduce the amount of CO2 produced. 

In the great majority of gasifier designs, all of these reactions occur in the same vessel, at temperatures anywhere between 700ºC and 1200ºC,  either in stratified layers or uniformly throughout a fluidized bed, as shown in the first sketch below.  It is a simple up-flow, fluidized bed design.  Other gasifiers may be packed bed, up- or down-flow, entrained or circulating fluidized beds.  With no further downstream gas processing, such a design, using air, can provide very hot, clean, partially burned gases, allowing a variety of solid fuels to be used with simple, efficient, normally-gas-fired boilers or kilns.  (For some commercially functionally examples, see  www.eneco.ca/   and  www.primenergy.com/Gasification_idx.htm )



( ‘Sorry  ‘bout the condition of this gasifier.   There was an explosion.   It’s currently shut down for repairs. )

For a higher quality gas (Btu/lb or kcal/kg), pure oxygen is used instead of air, avoiding the dilution by nitrogen.  Operating at higher pressures expands the range of process conditions and thus the range of product compositions. With the further addition of gas cleaning steps, the product can then be used in gas turbines or combined cycle (gas + steam) power  systems, for very high overall thermal efficiencies, to around 45%. (Planned plant: www.excelsiorenergy.com/mesaba/index.html)  With further gas conditioning and separation steps, a huge variety of applications is possible, as shown partially in the second sketch below.




In addition to simple combustion in a boiler or kiln, the syngas can  be fed to fuel cells to produce electric power at very high efficiencies.  Some fuel cells,  like the Molten Carbonate (MCFC)  designs,  require some re-forming to reduce or eliminate CO, which is toxic to their catalytic matrix, while others, like the Solid Oxide (SOFC) units, can accept the CO as a fuel.  Both of these produce a very hot discharge gas, as hot or hotter than gasification temperatures, containing un-reacted H2, which can be recycled to the gasifier, reducing the need for combustion and leading to even higher efficiencies. 

A relatively simple application, using different combinations of the concurrent reactions (above) to make methane, as Synthetic Natural Gas (SNG), as a cleaner use for coal. In the US, we have a successful producing plant  (http://www.dakotagas.com ) and an even more efficient process under development     (http://www.greatpointenergy.com/process.htm).

The greatest  -  and indeed, the most urgently needed  -  syngas application is  with Fischer –Tropsch (FT) conversion to a wide variety of hydrocarbons – primarily gasoline and diesel.  This is massive, complex but commercially proven technology.  South Africa, which has no petroleum resources, has produced up to 40% of its gasoline and diesel needs by this process, which also produces some methane and various alcohols. http://www.sasol.com/sasol_internet/frontend/navigation.jsp?navid=1600033&rootid=2

Processes under development include simplified versions of FT chemistry to produce ethanol from biomass of waste materials, far more efficiently than by the more-publicized fermentation processes, or mixtures of heavier alcohols  as higher  energy fuels.  http://powerecalene.com/index.html    All of the  reactions involved in methane synthesis and F-T conversions are exothermic, releasing heat that can be reclaimed to provide heat for the initial, endothermic pyrolysis and gasification reactions, thus reducing the amount of feed  consumed by combustion, thus reducing the CO2 produced per Btu or kcal of product.  An intriguing possibility that should be explored is the use of nuclear energy, in combination with a power plant, to provide all the heat to a gasifier, thus achieving maximum possible thermal conversion efficiencies and eliminating nearly all the CO2 emissions from the process.  

As a process design challenge, all of these applications require optimizing  the selection of operating parameters, to maximize yields of the desired product.  These parameters are –

  • Temperature

  • Pressure

  • Oxygen-to-feed ratio.

  • Steam-to feed ratio.

  • Ratio of recycled gases (CO and H2) to feed.

  • Residence time.

  • Choice of catalysts to promote desired reactions.

There are no reliable textbook formulas or methods to determine these factors.  Short of directly copying an existing plant design for the same feed material, every possible process design needs to be first defined  by some lab scale tests, either batch or (preferably)  continuous.  An example of an effective, small batch reaction system is shown below. 



Following bench scale tests to define chemical conversion performance, there remains the mechanical design challenge, to implement a commercially viable process.  For any commercial scale gasifier – either fluidized bed or settling (“fixed”) bed design - to achieve the process performance predicted by process chemistry alone, it must maintain uniform permeability or fluidization. Problems of bridging, channeling, plugging, or agglomeration into large, un-reacted lumps, cannot always be predicted by lab-scale process simulation, or may be predicted but eliminated by proper mechanical design.  Most bituminous coals and some biomasses, under certain conditions, present such problems.

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EXPERIENCE IN THE GASIFICATION & PYROLYSIS AREA


Designing  Fuidized Bed Pyrolysis Furnace, for Recovery of Energy and Products from Oil Field Wastes
.
    Process and mechanical design.

Coal & Biomass Gasification Process for Methane Production.
Lab scale testing, feed evaluation, process optimization.

Fischer-Tropsch Reactor for Coal-to-Liquids Plant.
Preliminary process engineering, reactor design and & equipment specification.

High Purity CO plant. (Methane reforming, DEA/MDEA, PSA & cryogenic separations)      Preliminary Process Design

Waste Tire Gasification / Pyrolysis, for Heat Recovery.
Preliminary processes design.

Ethanol from Wood, via Gasification and Fischer-Tropsch Synthesis.
Process analysis / certification.


Compact Methane Partial Oxidation, as Feed to Mobile Fuel Cells.  
Computer simulation and process optimization

Waste Wood Gasification with Dual-Fuel Engines or molten carbonate fuel cells.   Feasibility study and resource assessment for Minneapolis Metro area.

National Alternative Energy Assessment for Sri Lanka.
Gasification of rice hulls and wood for industrial heat, to replace imported fuel oil, with equipment specifications.

Pyrolyzed Lignite for Charcoal Cooking Briquettes in Haiti.
Experimental process development.

Pilot-scale coal gasification project – (Slagging, Pressurized, Settling Bed)      Operation, equipment modification and process reporting.

Super-Cyclone for Hot Gas Cleanup and Hydrogen Concentration.    Concept development and preliminary proof-of-concept experiments.

Measurement of Reeaction Rates and Catalyst Effectiveness in Coal Gasification.   Developed experimental apparatus and methods.

Catalytic Gasification for Integration with Molten Carbonate Fuel Cells.    Small lab-scale apparatus and method, for testing bituminous coals, lignite and wood with various catalysts.

Hydrogen Production from low Rank Coals by Catalytic Gasification.   Pilot and bench scale demonstration.

Measurement and Prediction of  Mechanical Properties (Density,  Shear Strength, Brittleness, Permeability, Thermal Friability, Abrasiveness, etc.) and Agglomeration Tendency of Coal and Biomass Feedstocks.

 Cold Simulation  of Fluidized Bed Performance 

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