Miracle weapon vegetable carbon
Coal makes the cow more tolerable for the climate. Not just any coal, but vegetable coal. Florian Gut produces such vegetable charcoal from wood. He has invested in a wood gasification plant for this purpose. In addition to the charcoal, a complex process also produces heat for heating several buildings and warm air for drying firewood. The heart of the plant is a gas engine that produces as much electricity in twenty hours of operation as a four-person Swiss household consumes in an entire year.
A striking wooden building stands in the hamlet of Desibach near Buch am Irchel. It smells pleasantly of fresh wood. "We constructed the building with wood from our own forest," says a visibly proud builder. Florian Gut is a farmer, vintner, entrepreneur, forest owner, plant operator, plant charcoal marketer and much more. "The project development took ten years until we were able to put the plant into regular operation in August 2021. We are very satisfied." Forests are a tradition in the Gut family. For generations, the family has managed about 33 hectares of its own forest. One specializes in the production of logs. "Every year, we produce about 500 stere of logs, which we can currently sell very well," explains Florian Gut. The new plant produces warm air for drying even larger quantities. The demand for logs is high, and the business line is to be expanded in the near future. Florian Gut thus confirms a nationwide trend: the use of logs in smaller plants in the home is being "rediscovered". People are spending more time at home and enjoying the healthy radiant heat of the wood fire.
However, the hot air dries not only large quantities of logs and chips, but also the wood chips for the wood gasifier. Large quantities of forest-fresh chips are stored in the chip silo, which are successively conveyed through the warm-air dryer and then reach an intermediate storage facility. From there, they pass through a refined mixing plant and are fed to the gasifier in the optimum composition (lumpiness, moisture). What is astonishing and striking is the great variability of the raw material. "We can actually feed all the assortments we have into the gasifier, which also means bark and fines from lump wood production. The gasifier is very tolerant in this respect," specifies Gut.
A tour of the plant is exciting and instructive. There is nothing of the romanticism of a wood fire. The installations are more like a large laboratory with countless pipes, containers, valves, measuring and control devices. Complex, electronically controlled and monitored feeding systems bring the fuel and later the combustion products to the right place at the right time in sophisticated processes.
This is how coal, electricity and heat are generated from wood
The pre-dried fuel - exclusively natural energy wood from the region - enters the pyrolysis reactor. At a heat of about 500 degrees, the wood is degassed and the first stage of coal is produced. The gas and coal then enter a levitation reactor, where further combustion air is added and the degassing process is completed at a temperature of about 850 degrees. The coal, which is now quite fine, "floats" in the gas stream to the filter, which separates it from the gas, cools it with the addition of water, and deposits it in big bags. The wood gas continues through a cooler, which lowers its temperature to about 100 degrees. It then flows through a water-operated scrubber and from there into the gas engine at a temperature of about 20 degrees. This roars in a soundproof cabin and has an electrical output of 240 kW. The engine has been running since August and in its first month of operation produced the same amount of electricity as about thirty four-person Swiss households consume during an entire year. Florian Gut receives a cost-covering feed-in tariff (KEV) for the electricity produced. Thanks to this subsidy, he can operate the plant economically. The heat generated during all steps of the process is recovered and used by means of a heat exchanger. As a result, the wood gasifier achieves a very high overall efficiency of more than 90 percent.
Coal, cow and climate
Now for the charcoal. Why all the effort to produce vegetable charcoal? A very broad, new field opens up here. Because vegetable charcoal is an exceptionally valuable substance. It can make a major contribution to improving the humus content and water retention of soils. It is also considered a carbon sink because it remains in the soil for a very long time - quite possibly several centuries. Florian Gut's farm is participating in a study conducted over several years by the Agroscope Agricultural Research Station on behalf of the Swiss Federal Office for Agriculture. It confirms the positive effects of plant charcoal on humus content (fertility), nutrient cycling (nitrogen) the water storage capacity and climate compatibility of intensively used agricultural soils. Plant charcoal acts as a sponge for nutrients and is a habitat for microorganisms. According to Agroscope, the "miracle weapon plant carbon" has another positive property: "The application of plant carbon can reduce nitrous oxide emissions (N2O) from agricultural soils, indicating a change in the activity of microorganisms in the soil. For the greenhouse gas balance of agricultural soils, the reduction of N2O emissions are of great importance, since nitrous oxide has a warming potential 300 times higher than CO2 has."
Florian well explains how the plant charcoal finally gets into the soil. From this, other advantages become apparent: "Vegetable charcoal as an addition to the cows' feed has a positive effect on the animals' digestion and well-being. It stinks less in the barn because ammonia excretion is reduced." This is also positive for the environment, as ammonia alters sensitive ecosystems such as marshes and forests. With the lower ammonia slurry, the plant carbon finally reaches the field and unfolds its positive effects in the soils over a very long time. For Florian Gut, the calculation adds up, since vegetable carbon is a sought-after and correspondingly high-priced raw material.
The Desibach plant is an excellent example of resource efficiency. It should find many imitators. Particularly suitable locations can be found wherever there is a high year-round heat demand of at least a few hundred kilowatts. For example, in large heating networks and especially in industrial processes that require a lot of heat.
The author wrote the article on behalf of Holzenergie Schweiz (cf. www.holzenergie.ch) authored.
Technical data of the plant Gut in Desibach
Manufacturer: Syncraft, A-6130 Schwaz, Austria
Plant type: CW 700
Dates: 2000: Idea; 2012: KEV application; 2016: Building permit; 2019: KEV approval; July 2020: Start of construction
Commissioning: July 2021
Fuel: Natural wood chips from the forest
Fuel consumption: approx. 160 kg / h
Thermal performance: 330 kW
Electrical power: 240 kW (nameplate gas engine)
Production coal: approx. 2 m3 per day, (160 - 200 t per year)
Water content coal: < 10%
Price coal: approx. CHF 1'000.- per tonne
Overall efficiency: > 90% Heat (heating, warm air) and electricity
