Zigzag Brick Kiln Design vs VSBK and Tunnel Kilns: Which Kiln for Which Plant

Zigzag brick kiln design forces air through a stack of bricks in a path about three times longer than a straight trench, which cuts fuel use by about 15–25% against a fixed chimney kiln (India’s BEE, 2022). A VSBK fires bricks in a vertical shaft with even less energy but small output. Tunnel kilns suit new large plants because they run all year and fire hollow units.

This comparison covers the three kilns that buyers usually ask about after the Bull’s trench and Hoffman kilns: zigzag, vertical shaft (VSBK) and clamp, set against the tunnel kiln. For Hoffman and Bull’s trench kilns, see Hoffman vs tunnel kiln. Most published figures below come from South Asia, including India’s Bureau of Energy Efficiency (BEE), because that is where these kilns have been measured. Each carries its source and year.

Zigzag Brick Kiln Design, VSBK and Tunnel Kilns at a Glance

The kilns differ most in output and product range, not only in energy: the two most frugal designs are also the most limited in what they can fire and how much.

The tunnel figure includes the dryer, while the others mostly assume bricks dried in the open air, so the 1.42 MJ/kg is not a like-for-like loss against the 1.11 MJ/kg of a zigzag kiln.

Zigzag Brick Kiln Design: How the Air Path and Layout Work

A zigzag kiln is a Bull’s trench kiln with the bricks reset so air weaves across the trench instead of running straight through it. The zigzag air path is about three times the length of a straight path (CSE, Zigzag Kilns: A Design Manual, 2017). Better mixing burns the fuel more completely, and the fire moves around a closed circuit through preheating, firing and cooling zones.

Three decisions set the design:

1. Draught. Natural-draught kilns rely on a tall chimney. Induced-draught kilns use a fan with a shorter chimney and a denser setting.
2. Trench width. This sets the number of bricks per chamber and therefore daily output.
3. Setting pattern. The CSE manual gives five lines per chamber with 5-inch gaps for natural draught, and six lines with 3-inch gaps for induced draught.

Source: MinErgy and the Federation of Nepalese Brick Industries, Rebuilding Nepal’s Brick Industry: Design Manual (2015), for a 230 × 110 × 55 mm brick. Other manuals give different pairs. The CSE manual (2017) lists a 33 ft trench at 44,000 bricks a day under natural draught, or 55,000 with a 15 hp fan. It gives 27 m as the minimum chimney height mandated for brick kilns in India, so local rules can override a design table.

The CSE manual also reports class I output rising to about 90%, from 55–60% in fixed chimney kilns, and coal use falling from 16 to 12 tonnes per 100,000 bricks. About 35% of the heat is still lost through kiln surfaces, so wall thickness matters: an 18-inch wall loses about three times as much heat as a 5-foot wall (CSE, 2017). The limits come with the format. The kiln is still an open-topped trench run by hand, fan versions need reliable power, and output stays small without an artificial dryer (BEE, 2022).

VSBK Brick Kiln: How a Vertical Shaft Kiln Fires

A VSBK brick kiln lowers batches of bricks through a fixed firing zone in the middle of a vertical shaft, recovering heat from both ends, which is why it has the lowest energy benchmark of any common kiln. Development Alternatives (1999) describes shafts about 1 m wide and 1–2 m long. Dried green bricks are loaded at the top in batches, normally four layers each, with powdered coal spread over each layer.

• Cycle. One batch is unloaded at the bottom and one loaded at the top every 2–3 hours, with 11–12 batches in the shaft and 24–30 hours for the full heating cycle (TARA, VSBK Design Manual, 2014). Development Alternatives (1999) reports cycles of 90–150 minutes.
• Heat recovery. Air drawn up from the bottom cools the fired bricks. Hot gases above the firing zone dry and preheat the green bricks. Peak temperature is up to 1,000 °C (Development Alternatives, 1999).
• Energy. Published values are 0.7–0.8 MJ/kg (TARA, 2014), about 0.84 MJ/kg (Development Alternatives, 2007) and a 0.91 MJ/kg benchmark from 13 kilns (BEE, 2022).

Why the vertical shaft brick kiln (VSBK) stayed small

The vertical shaft brick kiln (VSBK) stayed small because each shaft has low output and the kiln demands good green bricks and skilled operation. India’s BEE (2022) reports that about 100 were built and most are now not in use.

• Output. At 4,000–5,000 bricks a shaft each day (CSE, 2017), a 100,000-brick day needs 20–25 shafts (our estimate).
• Fixed geometry. The shaft is sized to one design brick and cannot be changed without rebuilding. A mismatch can cause jamming, shaft damage or heat loss (TARA, 2014).
• Sensitivity. Output depends on soil selection and green brick making (World Bank, 2020), and keeping the fire centered takes skill (Development Alternatives, 1999).
• Investment and perceived risk. The World Bank (2020) attributes low VSBK uptake in Nepal to inferior brick quality and higher investment per unit than other kilns, and Development Alternatives (2007) records that Indian manufacturers saw the technology as risky.

Clamp Kiln Brick Manufacturing

Clamp kiln brick manufacturing fires one stack at a time and then lets it go cold, so the heat in the bricks is lost after every batch. Green bricks and fuel are built into a large stack without a permanent kiln. The stack is lit, burns through and cools before it is taken apart.

The BEE (2022) benchmarks clamps at 1.79 MJ/kg, with audited coal-fired clamps from 1.35 to 1.95 MJ/kg and output of 0.6–1.5 million bricks a year. The World Bank (2020) calls clamps highly inefficient and, having no chimney, extremely polluting; they were banned in Nepal’s Kathmandu Valley several years before that country’s 2009 decision on kilns. Clamps also remain in industrial use in some markets: a University of Pretoria thesis (Akinshipe, 2018) tested a model clamp, holding 20,000–35,000 bricks per firing, at 11 South African factories.

Our judgment is that a clamp makes sense only as a low-volume, local, seasonal operation. CSE’s 2017 training material puts good-quality output at around 50–60% and notes that larger clamps are more energy efficient, but a clamp remains a batch process, and we see no practical route to automating it.

Energy and Emissions: What the Published Figures Show

Zigzag and VSBK kilns have the best published energy figures, and the tunnel kiln has the lowest limit in Nepal’s proposed 2009 table, but the particulate reductions claimed for zigzag conversion range from about 20% to 80% because the sources use different bases. Read the basis before quoting any of them.

The bases differ as follows. Nepal et al. (2019) measured stacks directly on a small sample of 3 zigzag and 4 straight-line kilns and report PM2.5 about 20% lower per kg of fuel and about 40% lower per kg of fired brick. India’s BEE (2022) gives “up to 50%” as a general sector figure. CSE’s 2017 training material gives 70–80% against fixed chimney kilns, with no test basis stated on the slide. We would treat the last two as published claims and use the per-brick measurement when comparing kilns. Across 13 kilns, Weyant et al. (Environmental Science & Technology, 2014) found differences of up to ten times by design, with an improved zigzag kiln among the lowest for PM2.5, and improved vertical shaft and tunnel kilns below the dominant designs. Our article on brick kiln emissions covers limits and controls.

Why New Large Plants Choose a Tunnel Kiln

New large brick plants choose tunnel kilns for output, year-round running and product range, not for the lowest energy number. Zigzag and VSBK kilns beat the tunnel kiln on the BEE’s 2022 energy benchmark, yet neither matches the rest of its case:

• Output. A single tunnel kiln reaches 50,000–400,000 bricks a day (BEE, 2022), while the upper part of that range is reached by zigzag and VSBK kilns only in multiples.
• Hollow units. Hollow and perforated bricks can cut clay and fuel by up to 50% against solid bricks, and high-perforation blocks are where zigzag kilns reach their limit (BEE, 2022). See hollow clay bricks.
• Control and automation. Each car follows the same firing curve, and setting and unloading can be mechanized. As a reference figure from Chinese practice, not a guaranteed specification, a tunnel kiln is at least 90 m long with a firing zone of about 40 m; the actual length follows the design. Our guide to the tunnel kiln for bricks covers sizing.
• Emission control. One stack and a controlled gas flow allow scrubbers, and US EPA AP-42 (section 11.3) reports hydrogen fluoride control of 95% or higher with a dry limestone scrubber at one plant.

Tunnel kilns have real demands too. Mechanized plants need reliable electricity and clay tested for extrusion, and about a third of kiln energy goes to the dryer (BEE, 2022).

The table below is our judgment from those figures, not a published ranking.

FAQ

What is the main idea of zigzag brick kiln design?

Zigzag brick kiln design sets the bricks so air weaves across the trench, making the air path about three times longer than a straight one (CSE, 2017). Longer travel and better mixing burn the fuel more completely. India’s BEE (2022) benchmarks zigzag kilns at 1.11 MJ/kg against 1.34 MJ/kg for fixed chimney Bull’s trench kilns.

What is a VSBK brick kiln used for?

A VSBK brick kiln fires small volumes of solid bricks with very low energy use. Batches descend through a fixed firing zone in a vertical shaft, and each shaft yields about 4,000–5,000 bricks a day (CSE, 2017). India’s BEE (2022) benchmarks it at 0.91 MJ/kg but reports that most Indian VSBKs are no longer in use.

Is zigzag better than a vertical shaft brick kiln (VSBK)?

In our judgment, zigzag is the easier step for most owners moving from a Bull’s trench kiln, because it reuses the existing trench and gives far more output per kiln. A VSBK uses less energy, 0.91 against 1.11 MJ/kg on the BEE’s 2022 benchmark, but needs consistent green bricks, more skilled operation and many shafts to reach the same output.

Can a zigzag kiln fire hollow blocks?

Only up to a point. India’s BEE (2022) reports that a zigzag kiln can be upgraded to make hollow and perforated bricks, but that blocks with about 50% perforation may not be possible. A plant whose market wants high-perforation blocks should plan for a tunnel kiln and test its clay for extrusion.

Does clamp kiln brick manufacturing still make sense?

Only for small local supply where regulations allow it. Clamps lose the heat of every batch, benchmark at 1.79 MJ/kg (BEE, 2022) and have no chimney, which the World Bank (2020) describes as extremely polluting. In our judgment, a new investor should expect stricter limits and should not base a commercial plant on clamps.

Why does a tunnel kiln use more energy than a zigzag kiln on paper?

The BEE’s 1.42 MJ/kg tunnel benchmark (2022) includes the dryer, which takes about a third of the kiln’s energy, while trench kilns usually dry bricks in open air. A tunnel kiln therefore pays for year-round drying that trench kilns get from the sun. Individual kilns also vary widely with insulation, gas tightness and firing time.

Planning a Tunnel Kiln Plant?

Our fired clay brick production line is built around a tunnel kiln, with kiln body design, refractory masonry and commissioning in the supply scope. The first step is a brick clay test, because the raw material decides the setting route and fuel plan.

Sources

• Bureau of Energy Efficiency (India), Energy and Resource Mapping of MSME Brick Sector (2022): https://beeindia.gov.in/sites/default/files/Brick_sector_Energy_Mapping.pdf
• World Bank, Dirty Stacks, High Stakes: An Overview of Brick Sector in South Asia (2020): https://openknowledge.worldbank.org/bitstreams/30c5bfb4-ea22-5e99-b0af-1eb35347f902/download
• Centre for Science and Environment (India), Zigzag Kilns: A Design Manual (2017): https://www.cseindia.org/zigzag-kilns-a-design-manual-8525
• Centre for Science and Environment (India), S. Kumar, Overview of Brick Manufacturing Technologies (training material, 2017): https://cdn.cseindia.org/docs/photogallery/slideshows/TP-cleaner-brick-production-20171211-15-Overview-of-Brick-Manufacturing-Technologies-Sonal-Kumar.pdf
• MinErgy and Federation of Nepalese Brick Industries, Rebuilding Nepal’s Brick Industry: Design Manual (2015): https://weadapt.org/wp-content/uploads/2023/05/design_manual_brick_kilns_nepal.pdf
• Development Alternatives, VSBK Technology: Brick by Brick (March 1999): https://devalt.org/newsletter/mar99/lead.htm
• Development Alternatives, The Vertical Shaft Brick Kiln: Cluster Development Approach for CDM (March 2007): https://devalt.org/newsletter/mar07/of_1.htm
• Technology and Action for Rural Advancement (TARA), Vertical Shaft Brick Kiln (VSBK) Design Manual (2014): https://devalt.org/images/L2_ProjectPdfs/Vertical_Shaft_Brick_Kiln_VSBK_Design_Manual%20.pdf
• S. Nepal et al., A Comparative Study of Stack Emissions from Straight-Line and Zigzag Brick Kilns in Nepal, Atmosphere 10(3), 107 (2019): https://www.mdpi.com/2073-4433/10/3/107
• O. B. Akinshipe, Atmospheric Emissions and Energy Metrics from Simulated Clamp Kiln Technology in the South African Clay Brick Industry, University of Pretoria (2018): https://repository.up.ac.za/handle/2263/64366
• C. Weyant et al., Emissions from South Asian Brick Production, Environmental Science & Technology 48(11), 6477–6483 (2014): https://doi.org/10.1021/es500186g
• US EPA, AP-42 Section 11.3: Brick and Structural Clay Product Manufacturing: https://www.epa.gov/sites/default/files/2020-10/documents/c11s03.pdf
• Brick Industry Association, Technical Note 9: Manufacturing of Brick (December 2006): https://gobrick.com/media/file/9-manufacturing-of-brick.pdf