Vertical Shaft Brick Kiln

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Vertical Shaft Brick Kiln, VSBK in Chambo, Ecuador - Horno Vertical Continuo HVC

Basics

Updraft kiln for firing clay bricks. High fuel economy (coal, biomass). Low space requirements. Produces high-quality bricks. Open source!

About

Origin: VSBK technology is not patented. Since its commercial, environmental and social development was financed by SDC (Swiss Agency for Development and Cooperation), this technology is considered open source. The concept was originally developed in China in the late 1960s during the cultural revolution. In some ways, its development parallels that of the Chinese Greenhouse: a rural, medium-scale technology that was later strongly supported by government and academia, leading to many small technical improvements and massive roll-out.

Principle: Updraft = heat is reused. This operating principle is similar to that of a vertical shaft lime kiln. Cold air entering at the bottom cools down the descending (fired) bricks, is then used for firing, then warms up the still-cold bricks on top of the stack. Bricks are loaded at the top and removed at ground level in a continuous process (see animation below for details).

Energy: Most energy efficient brick kiln there is. Combines low cost of updraft firing with high fuel economy. Said to be twice to three times as energy efficient as Hoffmann kiln. Energy consumption figures (China): 0.103 kg coal per brick or 975 MJ/kg per 1000 bricks. Usually fired with low-grade coal fines, but may be adapted to other fuels. Firing shaft is very well insulated on all four sides, minimizing heat loss.

Output: Each batch of bricks is made up of four layers, making a total of 320 bricks per batch. Many of these kilns put out 10,000-15,000 bricks per day (this figure may refer to a 2-shaft kiln). Quality is very high and brick wastage is very low when compared to other kilns, being only 2-5% in China. The firing process is completed in about 24-30h as the bricks move from top to bottom. One batch is removed at the bottom at a regular interval.

Versatility: Well suited for firing solid bricks. Works with hand-molded bricks or extruded bricks, even non-standard shapes as long as the stability of the stack is assured. It can also be used to fire bricks with perforations, but is not suitable for firing hollow bricks or thinner products like tiles (although attempts are being made in this direction).

Videos

Related Pages On This Wiki

Pros and Cons vs. Compressed Earth Blocks

Pro:

  • no liquid fuel (e.g. diesel, gasoline, ethanol) or electricity needed that would otherwise be required for the CEB press; energy savings due to lower-grade fuel, no need for liquid fuel distillation
  • uses low-cost / low-quality fuel such as coal fines or charcoal fines, possibly pyrolysis gas from other processes (see development proposal below)
  • carbon negativity more easily achieved (if part of a Biochar/Brick Co-production System)
  • possibility to re-use waste heat (space heating for applications such as greenhouses, fish tanks, etc.)
  • no stabilizer needed (e.g. cement, lime, flyash, etc.), leading to energy savings.
  • reduced wear and tear on the infrastructure per brick (volume is large)
  • possibly more stable and more weather-resistant bricks (this requires comparisons, lab testing)
  • CEBs may not be suitable for all applications anyway (e.g. where they are exposed to a lot of water), so an alternative is needed. Fired bricks are a good, proven alternative.
  • bricks are of consistently high quality (in fact, they HAVE to be, because of the compressive force that they have to withstand for the stacking)
  • likely less work needed per brick for handling (one of the links below describes the labor requirements thusly: "Labour requirements are low, requiring one man to load and two men to unload, during an 8 or 12 hour shift. The laborers are not working continuously, as there are 3 or 4 hours between each loading/unloading session.")
  • less need to monitor bricks over weeks (e.g. curing of CEBs with moisture monitoring etc.)

Con:

  • possibly increased fuel use per brick. This is not certain, as the VSBK is very energy efficient, and the fuel use for CEBs is not zero either. Calculations are difficult because of very different fuel types.
  • a larger installation means less flexibility (this facility is not easy to move, in contrast to CEB press, although moving the kiln has actually been done in China)
  • potential air pollution problems (this is largely a factor of higher volume/concentration of production)
  • requirement for continuous operation on nights/weekends (there are breaks though - see labor requirements under "Pro")
  • VSBK is only for the production of bricks. Tiles would have to be fired in some other way.
  • need for a well-trained, skilled "brickmaster" who is able to keep the fire at the right level and intensity
  • possibly more stringent requirements for suitability of clay

Income Potential

  • At a realistic market price of $0.5/brick, 10,000 bricks per day = $5000/day gross revenue (minus labor costs, minus fuel costs, minus amortization, etc.)
  • output of 3 million bricks/year = ~$1.5M revenue
  • construction cost for one such facility (standard, coal-fired) in India about $60,000-80,000 (2013 publication by SKAT, see below), depending on configuration.
  • amortization cost is low, considering an expected operational lifetime of 15 years
  • fuel costs may be minimal if waste biomass is used (wood, straw, other biomass)

Development Proposal

(see page: Biochar/Brick Co-production System)

The typical VSBK is coal-fired, mostly using low-quality coal fines. As shown in the (Vimeo) animation above, pieces of coal are scattered onto the bricks from the top. Since coal is a polluting and sometimes unavailable fuel, the proposal here is to develop a (carbon-negative) VSBK fired with pyrolysis gas (with biochar as a co-product). Some reports suggest that wood chips and crop waste can be used as fuel instead of coal fines, but it is not clear how that affects the whole process.

  • The brick kiln could be re-designed as part of a combined system to run on the pyrolysis gas, a byproduct of biochar production. In such a system, the hot pyrolysis gas would be blown into the kiln from the front and back, through the 5 or so holes in the bottom layer of each brick stack.
  • This gas-fired kiln would have cleaner emissions than the coal-fired one (less: soot, heavy metals, organic pollutants, etc.). The off-gas could conceivably be used for CO2 enrichment in a greenhouse or garden/field (this may require a biofilter step first).
  • Co-products in addition to bricks: biochar, heat, CO2-rich gas for greenhouses.
  • higher expected cost: A pyrolysis gas fired facility will likely be somewhat more complicated and expensive than a coal-fired one.

Further Information (links)

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