Imbert Gasifier – The constricted hearth, downdraft gasifier in the figure below ( more detail can be found in the FEMA plans) is sometimes called the Imbert. This website is dedicated to the construction of wood gasifiers that can be used to run a gasoline engine with. Woodgas has been around for a long time and it. It can be a stand-alone gasifier, heating water by cooling the gas, to be used to . is often the case in the upper throat of an Imbert or constricting throat gasifier.

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Clean, Efficient Waste-to-Energy System. This is a completely new design, based on the best of my previous prototypes. For more details on my previous work http: This gasifier design is the culmination of my 42 years of work on this technology, and I think it will solve many of the problems that now plague those modeled after the old WWII gasifiers.

While many recent improvements have been made by dedicated gasifier enthusiasts, it is still an evolving technology, with much scope for new approaches and improvements in the utilization of huge quantities of locally-available waste gasifir and hydrocarbon fuel sources.

Biomass- and waste-fueled energy has the potential to contribute gasigier more to global green energy demands. Imbfrt prototype embodies optimized gravity flow principles that follows more elegant thermodynamics than previous approaches, concentrating air, gas and imbsrt flow into ibert central gasification reaction through an interweaving of concentric shells and spiral ducts, to create a clean gas of significantly higher heat content.

Most furnaces are rated at Low Heat dry weight basis efficiency, discounting the agsifier in the wood, since condensation does not occur, thus losing the heat of vaporization. Since green biomass can often i,bert half water, and the other half of bone-dry wood combusts with more Oxygen from the air into more-than-its-weight of additional water vapor! This represents a significant increase in energy available from condensing the woodgas or exhaust.

This and the exhaust-scrubbing advantage to condensing the exhaust is the reason the heat-exchanger on this furnace is so huge 84 sq. There will be an operating range where the gas is the cleanest, and another condensing range where efficiencies of both gas and hot water production are highest, and an upward range where exhaust is too hot to condense.

These parameters will have to be tested to know for sure. Ideally, anything that will burn can be vaporized or gasified and turned into a fuel. Ideally, the Nitrogen Oxide NOx content is very low, and soot, hydrocarbons and other smoke pollutants are non-existent. The steam can mostly condense on grains of fly-ash and the cleansing rain will scrub the gas clean in a properly designed HX.

However, the difference between ideal and practical has been significant in the history of gasification, largely because waste fuels are not homogeneous and measurable like gasoline and natural gas. The pieces gasify at different rates, and the difference in moisture, ash, elemental composition, slagging temperature, oxygen imberrt CO2 penetration of the coal-bed, feed considerations, etc.

These challenges have been grist for my explorations into this technology.

Design of downdraught gasifiers

Roundy has been designed from the following. Air and gas flow throughout this system is governed by fundamental principles of gravity, temperature and density. Refer to the above drawing for orientation.

Warm regards, Larry Dobson lad fundamentalform. These plans are offered to you FREE. I depend on your generous support! Read about the development of this technology and former prototypes at http: In background is involute spiral VAWT on hat. Fuel in a hopper gasifies best and most evenly, without bridging, when it is burned, vaporized, gasified evenly at the base of a vertical-sided hopper.

Whenever there is bridging of the fuel, air supports combustion beneath the bridge, creating hot flames and a spent gas with excess oxygen and little if any energy value. If the bridge burns through, the gas is greatly diluted and cooled by excess air, which can totally rob the fuel gas of energy.

Then the bridge collapses, quenching the flames and heat with cool damp fuel and steam, creating a burst of sooty gas, followed by diminished cool gas production. Providing the above feed conditions are addressed, preheating the incoming air can almost entirely solve this problem, if it is hot enough, because the endothermic gasification is sustained in a deeper coal bed by the high-heat of a lesser volume of air.

This is quite different from conditions created by a larger volume of cool air, with its oxygen content creating combustion to supply the heat along with lots of diluting nitrogen and CO2. With this approach, higher-energy-content-gas can be created.


Of the three fundamental thermodynamic ingredients of Time, Temperature and Turbulence, Time is too often neglected in favor of Turbulence, as in the jet of speedy air shooting from the tuyers of a downdraft gasifier. I have found it better to let the air slowly permeate the fuel, heating up a large mass of fuel slowly, evenly, creating a large hot coal-bed, letting the gas become saturated with CO and Hydrogen over time and temperature.

Instead of turbulence for mixing and HX efficiency, Roundy has been designed for laminar and internal vortex currents propelled by natural convection flow.

Steam and CO2 are primary combustion enhancers, speeding heat transfer significantly by their bipolar molecular property of absorbing and radiating radiant energy. Radiation is the primary mode of heat transfer at the temperatures of gasification. N2, O2, CO and H2 do not absorb radiant energy, so heat transfer must come from neighboring bipolar molecules or be delayed.

Imbert Gasifier

The best gasifier utilizes these reactions optimally, along with preheating the fuel and air, for a high energy gas. There appears to be no theoretical gasifieg to how much water can be turned into fuel gas, as long as gasfier and time are sufficient for the reaction.

Contrary to expectations, adding all this heat and insulation does not deteriorate the materials of construction as much as allowing local hot spots of ,F combustion, which is far above the required gasification temperatures of – F. Temperatures above F rapidly oxidize metals and thermal-shock ceramic, as when cool fuel suddenly lands on orange-hot refractory or cool air rushes in an empty open hopper.

Solid fuel gasification and combustion produces ash, which collects on all horizontal surfaces, blocking passageways and requiring cleaning. As much as possible, design gaeifier, furnaces, heat exchangers with only vertical surfaces….

Design ash-collecting areas to be easily cleaned. When burning the gas to heat water, the generated gas is burned in a concentric combustion shell, which feeds heat to the incoming air and fuel in the hopper, augmenting the calorific value of the produced gas, thereby requiring less air for more gasification of a higher quality gas, which is mixed with preheated air and burns super-clean in the combustion shell.

Highly preheated gasification air is introduced to the preheated fuel around the base of the hopper, where it is burned and gasified, creating a steady-state fuel feed without disruption of the fuel. Residence time of all heat transfer and chemical reactions can be much greater than conventional practices, which greatly expands fuel options. Since this first version of the gasifier has a thin-shelled ceramic hopper lining, large heavy chunks of fuel should not be dropped in, especially without a cushioning coal-bed.

Testing of gzsifier prototype will indicate whether a lighter, thinner stainless steel hopper will withstand the internal temperatures. A conical grate at the base rotates to dump ashes imbeert break up gaisfier bridging. Biologically-activated biochar is a major discovery in soil fertility, which can make the family farm more productive, just from the waste biomass accumulated around the farm. It must be inoculated with mycelium to become activated for plants.

When a fluid is heated, it expands, gets lighter, and travels upward, augmenting natural draft. When a fluid is cooled, it contracts, gets heavier and travels downward, also augmenting natural draft. When these principles are adhered to, the strongest natural draft is facilitated, pumping throughout the system without a fan although one may be necessary for starting and increasing the throughput and responsiveness of the system.

When these principles are incorporated into a counter-flow heat exchange, the hot fluid being cooled flows fastest downward next to the heat-exchange surface, and the cool fluid being heated flows fastest upward next to the heat-exchange surface. This increases heat transfer greatly by decreasing the boundary-layer of insulating fluid next to the heat-transfer-surface and allowing gravity-stratification, which increases efficiency as throughput is reduced, increasing residence time for greater temperature gradient.

This principle is extremely important for efficiency, quality of gas, cleanliness ombert burn and greatly extended turn-down ratio. This means that a larger system is actually more efficient when ggasifier down. Adhering to these laws of flow means that the most efficient system has the exhaust exiting from the bottom of the furnace, not the top, and the natural draft created throughout the system can be so strong as to eliminate the need for an outside chimney.

This is impossible when turbulence takes over. This removes heat from the bottom plate and bottom of ash-shell, preheating the air. The air then travels up outside the ash-shell, extracting more heat, then enters the ceramic duct next to the combustion shell, where it is heated by the burning gas or F hot producer-gasrises up over the ceramic shell to the inside, then travels down next to the cooler hopper shell, heating the fuel inside as it flows.


The hot primary air exits at the base of the hopper, where it volatizes the fuel and moisture and burns it until the oxygen-starved gas travels down through the coal bed. The chemical reactions at this gasified are all endothermic, taking gasifir away from the hot gas and charcoal as more combustible CO and H2 are liberated.

There are many variables for different fuels, so we may need to develop several modular grate designs to provide an even gasification rate through a uniform coal bed of the depth to optimize woodgas production or biochar. The fuel gas can be generated cooler and wetter and sootier for direct combustion it all burns clean at the right temperature and residence time, with the right amount of air mixed evenly.

Within the turn-down range of super-clean combustion, there will be a narrower optimum range for production of a clean gas for I.

The cooler, but still hot, woodgas producer gas, biomass gas, garbage gas exits from the hearth through the central conical grate, between conical slats that provide large openings that prevent the fuel from falling through because they provide overhanging ledges. This design has proven quite superior to just holes, which let through small aggregate fuel particles and easily get clogged with charcoal and ash. The grate is adjustable up and down to optimize the charcoal depth, and can be agitated by turning to drop out ash and biochar if that is also wanted.

Ash collects below, where it can be removed through the front access door. The hot fuel gas then flows gasicier the four woodgas-to-combustor-ducts at the top of the ash bin. Most of the ash is deposited here, since the gas must turn degrees to flow upward, while the ash falls gasitier gravity. In the annular combustor ring, when in combustion mode, the hot gas is mixed with secondary air, where it burns cleanly due to hot temperature and even mixing of gas and air.

The secondary combustion air enters two dampers in the bottom plate, where it is heated by the primary air shell, also cooling the lower region and saving on insulation.

The combustor preheats the primary gasification air, which creates a higher quality gas while lowering gasifief temperature of combustion, which reduces deterioration of materials and lowers levels of NOx pollutants. The outer shell of the combustor is insulated from the heat exchanger HX to facilitate optimum combustion and maximum HX efficiency. If the system is being operated as a gasifier, no combustion air is introduced and the hot producer gas performs the same heat-transfer function, although not as intense as when combustion is present.

At the top of the gasifker the exhaust or producer gas enters the spiral HX through an annular duct, which distributes the gas evenly around the entrance to the HX.

The spiral HX consists of a spiral water duct with a larger spiral gas duct in between. The gas is cooled by ft2 of water-cooled surface area, which causes gravity stratification of the gas as it gets denser and falls next to the water jacket, while the opposite flow occurs within the water.

It is expected that, when operating in this condensing mode, the producer gas can be directed straight to an internal combustion engine without the need for further filtering.

Condensate water is drained out at the base.

The interior hot zones are either cast-ceramic or high-chromium stainless steel, I have incorporated ceramic parts in the hottest parts because my experience has been that stainless steel deteriorates too fast.

This furnace will weigh around lb, with lb of that being refractory ceramic. To put things in perspective, consider the advantages of being able to produce both hot water and woodgas at higher efficiencies and cleanliness, with a greatly extended range of usable fuels and energy output. This design with all the interrelated heat-feedback features is where I want to begin testing, but many design variations, degree of refinement, much larger and smaller units, vehicle gasifiers, etc.

More pix and updated drawings to come!