RP Siegel

Are Today’s Leaves Tomorrow’s Energy?

Researchers at Virginia Tech recently showcased a 10kW demonstration biomass power plant. The plant, which burns syngas, derived from biomass feedstock, such as wood chips, corncobs, manure and other agricultural waste, powers a three-cylinder internal combustion engine which generates 1 kWh for every 1.2 kg of biomass.

Professor Henry Quesada-Pineda works at the Wood Enterprise Institute, which is part of the Department of Sustainable Biomaterials. He said the institute purchased the unit to demonstrate the use of biomass to generate clean energy, to conduct research to see if they can extend the range of feedstocks, to include things like food waste and finally to incorporate it into the curriculum. They purchased the unit from ALL Power Labs, that makes small gasifier experimental kits for educational purposes, as well as fully automated Power Pallets, up to 20 kW that are currently sold in 30 countries.

That led me to wonder who else is making small scale, portable biomass power plants. Is this a trend that might actually catch on? Will our autumn leaf rakings end up powering the Sunday afternoon football game on TV?

This is not a new idea. In India, there is currently 160MW of off-grid, small scale biomass generation capacity. Not surprising in a place where biomass provides 32% of the primary energy as well as significant employment. The Ministry of Renewable Energy estimates availability of some 500 millions metric tons per year. Much of that is used in large scale projects. But the Ministry also launched a “Power for All” program that brought gasifier technology to tiny villages.

There are many ways that biomass can be used to provide energy. Back here in the states, much of our biomass goes into biofuels, ethanol, in particular.

What About Electricity?

But what about producing electricity directly from the stuff? There are three primary ways to do it, utilizing combustion, gasification or pyrolysis.  The difference between the three is primarily a matter of the amount of oxygen, temperature and time given to each process.

A web search turned up a variety of small scale portable biomass generators. Depending on what you consider portable, AgriPower has a system that mounts on the back of a tractor trailer truck. Available in power ranges up to 2.2 MW; it’s essentially a pre-fabricated system, consisting of 9 modules that can be quickly put together on a gravel, or cement lay-down pad. It burns the biomass along with other waste materials such as plastics, to produce heated products of combustion that are fed into a 125kW waste heat generator. The system can also provide hot air, hot water or steam in a variety of combined heat and power (CHP) applications.

Cyclone Power also uses a combustion waste heat engine, though their product utilizes a unique external combustion, radially-configured steam engine invented by company founder Harry Schoell, that can use any fuel without modification, while achieving thermal efficiencies over 30%, and which, according to their claims, produces zero emissions. The engine won the Popular Science Invention of the Year Award in 2008. They are in pre-production at the moment, though they claim to be very close to a production. The water for the steam is continuously recycled. Besides generating electricity, they claim this engine can substitute for any other engine application including vehicles or heavy equipment, any of which can run on any fuel.

An Irish group has developed a prototype of a thermoelectric converter to be used in conjunction with a biomass cook stove, suitable for use in developing countries. Thermoelectric devices turn heat directly into electricity.

British company Talbott’s has been making small biomass powered generators for 30 years. They have installed over 4,000 systems worldwide, ranging from 25 kW to 10MW and can produce both electricity and heat using primarily wood as the feedstock. That’s a bit large for your backyard, but the smallest units might not be too big for some homes. These are basically traditional steam generators with wood (instead of coal or gas) fired boilers, which does save a significant amount of CO2.

Examples of Combustion

All of these are examples of combustion. This is popular because of its relatively low cost and simplicity. Gasification is more expensive but also more efficient. It can produce both Syngas and bio-methane. Bio-methane is produced through anaerobic digestion, where bacteria break down organic matter, in the absence of oxygen, producing methane as a byproduct. This is often used in landfills, though it can also be done on a small scale. Home-made units are popular in some parts of the world. Syngas, or synthesis gas, which is what All Power’s unit produces, is made in an environment where steam, and/or oxygen is added to the organic material in a carefully controlled manner. Primary outputs are hydrogen and carbon monoxide. Larger versions of these systems are made by Broadcrown.

Finally, there is pyrolysis. Pyrolysis is a process which uses heat in the absence of air, to break down organic matter. Pyrolysis can create byproducts in the form of gas, liquid (oil) or solid (char). Both pyrolysis oil and Syngas are considered intermediates between biomass, from which commercial products (e.g. ammonia, hydrogen) are made, though both can be used, as is. Biochar is being hailed as a major weapon in the battle against climate change with triple benefits because it can be considered carbon negative, provided it is derived from a sustainable source. Biochar can also help restore degraded soils, improving nutrient uptake, while producing gas and oil that can be used to fuel the process.

These technologies are widely used in other parts of the world. Whether they should ever become popular here in the U.S., for those with access to biomass, remains to be seen.

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