The CHP acronym means "combined heat and power".  In layman's terms, it is a system to use wood to generate electricity, heat and/or hot water (or any combination of two). 

Some History
Since gasoline and petrol fueled generators have been so cheap, not much attention has been paid to woodgas technology.  However, a similar technology was critical to some countries during W.W.II for transportation.  In Wartime Europe, petrol became very expensive and sometimes was only available for the military.  However civilian tractors and trucks still needed fuel to operate so commerce (especially food production) could continue.  So "gasifier" units were designed, constructed then bolted to the sides of many vehicles.  The units were dirty, stinky and temperamental but they were sometimes the only non animal means of transportation grade energy. 

During the last oil embargo, some companies dusted off this technology.  They found that a properly designed gasifier can be cleaner and more efficient at extracting wood heat than a typical stick burning wood stove.  They are usually employed to provide a low grade gaseous fuel to use in a burner for heat or in an engine for producing heat,  mechanical or electric energy.  However, gasifiers appear to have significant problems.  One problem is that a gasifier typically has a large startup time.  A good design might start in five minutes but a half hour may be required to reach full power.  Gasifiers also don't like to quickly change the amount of power produced.  This might make them suitable for running a steady vehicle load such as a tractor, but an automobile in stop and go traffic would have sub par performance.  Also, tar, acid and abrasive ash production make engine life much shorter unless extensive filtering and maintenance are done.

A Technology That Still Has Possibilities
These problems make a gasifier a poor choice for fueling a vehicle except in the most dire circumstances.  However, these problems are not as limiting in a stationary CHP unit.  For units employed heating hot water, sudden energy draws are provided by the water tank instead of the CHP unit.  For units employed in building heating, only gradual power changes are usually needed.  Some CHP units can also provide steady electric capacity too.  At the small scale, the cost per watt of power is not cheap.  A complete gasifier system can cost thousands to build - and only provide the same amount of electric power provided by a gasoline generator costing hundreds.  However, if the price of fuel is entered into the total cost of ownership, small scale gasifiers may become more attractive than natural gas heating or oil fired systems - plus they might be able to supply backup electric power too! 

Building A Small Gasifier
A few people still build gasifier units as a hobby  - attracted by the potential for low cost fuel.  Such renewable systems have several advantages over solar and wind.  First, a gasifier should be cheaper to initially build on a per watt basis than a small PV system of equivalent power.  Unlike solar or wind, they also don't need a sophisticated storage system for energy for cloudy, cold or windless days.  They can also (in theory) be made from materials that can be found near typical small towns. 

To investigate woodgas, my original plan was to build a small batch gasifier to see what the issues are.  The gasifier would have been a downdraft design made out of pipe fittings based on the Fluidyne Pioneer Class gasifier design  The wood gas would then be cleaned and burned in an internal combustion engine.  The engine, in my case, would have driven a 5 HP Tecumseh (or Briggs and Stratton) engine. Once controlled combustion was demonstrated, a mechanical load such as a generator or water pump could then be attached to it to demonstrate mechanical power ability.  The untried part of the plan was to power the system using wood pellets rather than wood chips. 

What I found during my research phase was that the logistical problems are just as important to address as the technical ones. For me, I have concluded I currently lack the land resources to build a project at a useful scale using Woodgas. For example, many areas have zoning that effectively prohibits ever being able to test such a unit within town boundries.  Carbon monoxide poisioning, explosion, fire hazard, toxic byproducts and production of useless junk from worn out parts are all problems.  Fortunately, some modern day innovators have taken up the challenge.  Below are some terms that can be used to develop a vocabulary to talk to these innovators.

WOOD GAS AS AN ENGINE FUEL -  FAO forestry Department
Say what you want about the United Nations, but occasionally they do some good.  This is a good introduction on the issues of converting vehicles to gasifier power.  Some of the formulas are not quite as clear as they should be but you should be able to get a general idea of what is going on.  If you are seriously contemplating making a vehicle run on woodgas, this should be required reading so you can be familiar with the terms used.  It covers the gasifier, cooling and filtering.  It also includes an analysis that asks if converting a truck to woodgas would be "worth it". I'm not sure if this publication can be ordered - but it can be read online HERE.

GENGAS: THE SWEDISH CLASSIC ON WOOD FUELED VEHICLES - BEF foundation
A rather thick book that describes the history of wartime gasifiers and the politics behind their use.  It also has some technical information that might be useful for the would-be constructor of an Imbert gasifier. The W.W.II designs may not be the best ever, but they are "proven" technology.  The gasifiers should be able to be built with handyman knowledge and metal working tools available via retailers such as Harbor Freight. The book emphasizes gasifier and filter construction rather than modern engine conversion.  Since most modern engines use fuel injection, a modern engine would need to be severely modified before it could run on wood.  However, this book along with an engineering degree, a really well equipped machine shop and a fat bank account might allow you to build that wood powered vehicle you've always wanted.

BIOMASS DOWNDRAFT GASIFIER ENGINE SYSTEMS HANDBOOK - BEF foundation
Another book filling in gaps where GENGAS left off.  Lots of ideas on how to measure gasifier output and refine gasifier designs.  If you get Gengas, pick up this one too.  In the proper hands, it would probably save some time when designing a gasifier.

PRODUCER-GAS: ANOTHER FUEL FOR MOTOR TRANSPORT - BEF foundation
A really basic booklet introducing the concept of gasification.  Save your money.  There is nothing here you can't get from the other books on this page.

FUNDAMENTAL STUDY AND SCALE UP OF THE AIR-OXYGEN STRATIFIED DOWNDRAFT GASIFIER: - BEF foundation
For those who really want to push the gasifier art to new levels, there is this book.  It describes a "new" type of gasifier called the stratified gasifier.  It is clear some major research money went into writing this book.  The technology looks promising - yet the book is far from a how-to guide.  If you are looking for thesis material, or possibly an idea for getting millions in government grants, this may be your book.

CONSTRUCTION OF A SIMPLIFIED WOOD GAS GENERATOR - BEF foundation
This describes an "emergency" stratified gasifier.  Although it looks simple, it is NOT something you want to be constructing during a crisis!  Build one of these units BEFORE you need it to see if it even works!  (there are conflicting accounts on if this simplified stratified design works or not)  Another problem is that some of the "common materials" mentioned are actually not that common anymore!  For example, the project requires a pair of galvanized oil drums and galvanized pipe nipples.  Drums of that nature are now special orders and most hardware stores only carry PVC parts!  Still, most items should still be available via the Internet.  Purchase from BEF or look online for FREE!

About the author: 
The author of this page is William McCracken - a disclaimer for this site can be found HERE  last updated 9-25-2005