Introduction

The use of fired ceramic bricks goes back more than three thousand years, and bricks are still the preferred house construction material in most countries around the world. In many countries, the brick industry is the largest single user of energy and also employs a large number of workers, due to the labour intensive manual brickmaking process. Suitable clays for manufacturing bricks exist almost everywhere, and the brick-making process can be done with simple manual methods, or in highly automated plants, depending on the prevailing labour cost and the demand of the market.

Firing the bricks, also termed baking, gives them strength and turns the plastic clay irreversibly into a permanent hard material that can no longer be slaked in water. Originally, bricks were fired in clamps or scove kilns. These are not permanent structures, but simply a pile of green bricks covered with a sealing layer of mud, with the fuel placed under the bricks. Later, permanent kilns were used for firing bricks. Both types of kiln are loaded with green bricks, which are heated up to the desired temperature and then cooled again before the bricks can be drawn from the kiln. All the heat energy used for firing is lost during cooling, and such so-called periodic kilns waste energy.

The Bull's trench kiln

The kiln can be made circular or elliptical in shape. It is constructed on dry land, by digging a trench, 6 - 9 m wide, 2 - 2.5 m deep, and 100 - 150 m long. An alternative method is to build up the sides of the kiln with bricks, especially where drainage is a problem. Gaps are left in the outer wall for easy assess to the trench during setting and drawing of bricks.

The green bricks to be fired are set in rows, two to three bricks wide, with holes in between that allow feeding of coal and a sufficient flow of air through the setting (Figure 2). A linking layer of bricks is made across the width of the kiln and half way up, to stabilize the setting. On top of the bricks, two layers of bricks, covered with ash or brick dust, seal the setting. A large piece of canvas, paper or metal sheet is placed vertically across the brick setting to block air from entering from the wrong side of the chimneys (Figure 3). The trench contains 200 - 300,000 bricks at a time.

Chimneys, 6 - 10 m high, made of sheet metal, are placed on top of the brick setting. They are moved around as the firing progresses and they have to be light, so that the firing crew can carry them. Wires attached to the top of the steel chimneys support them. The need for lightness and the cost of replacing the chimneys often have the effect that the height of the chimneys becomes too low. That means the exhaust temperature has to be higher in order to maintain sufficient draught and the chimneys are placed closer to the firing zone. Thereby, less heat of the exhaust gases can be reutilized. Small circular Bull's trench kilns use only one chimney, whereas the larger elliptical kilns need two chimneys.

The firing in a Bull's trench kiln is continuous, day and night. Green bricks are loaded and finished bricks are drawn all the time. The fuel saving is achieved by reusing part of the energy that is otherwise lost in periodic

kilns. As shown in Figure 4, the air for combustion is drawn through the already fired but still hot bricks. The cooling bricks transfer their heat to the combustion air, pre-heating it before it enters the firing zone. After combustion, the hot exhaust gases pass through the yet unfired bricks on their way to the chimneys. This pre-heats the bricks, so less fuel is needed to bring the bricks to the maximum temperature. Once every 24 hours the chimneys are moved forward 5 to 7 m. Daily output is 15 - 25,000 bricks.

Figure 2

Design of a Bulls trench kiln

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Required manpower and fuel

Normally, the firing crew consists of six men organized in two teams, who take turns stoking the kiln. When the chimneys are moved, all six men are needed. The whole operation of shifting the chimneys forward takes about one hour.

The firemen stoke the fire through removable cast iron holes at the top of the brick setting. Ideally, stoking should be done 3 - 4 times per hour, but especially at night, the workers tend to stoke large amounts of fuel at long intervals, causing an increase in fuel consumption. The firing of the kiln demands great skill, which may take years to master well. The fuel can be any

combustible material or a combination of them; coal, lignite, peat, firewood, saw dust, agricultural waste, such as rice husk, brand or coffee shells. Natural gas or oil can also be used, but such fuel is normally too expensive. Old tires cut into pieces are more commonly used, but the combustion gases are very toxic, and in many countries the use of tires has been banned.

Figure 3

Fired bricks being drawn from the kiln (Pakistan)

Figure 4

A canvas prevents air from entering the kiln from the wrong end (Pakistan)

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Chimney

There are two main drawbacks with moveable chimneys;

the metal sheets are eaten up by corosion within 1.5 - 2 months, and during the time it takes to move the chimneys, the temperature drops.

This loss of temperature increases, fuel consumption by about 5 - 10%. In the dryer areas of the Indian subcontinent, a Bull's trench kiln with a fixed central chimney is now widely useed (Figure 5). Compared to the moveable chimneys the initial cost is higher, but the saving the cost of replacing the metal chimneys and the slightly better fuel economy soon pays back the initial investment. A large central flue channel is constructed in the centre of the elliptical kiln, and through this, the exhaust gases flow to a brickwork chimney. Where electricity is, available and in stable supply, an exhaust fan can be used instead of a chimney.

Figure 5

A Bulls trench kiln with a fixed chimney (Pakistan)

Advantages of the Bull's trench kiln

More fuel efficiency compared to periodic kilns. Low initial investment. High capacity.

Disadvantages of the Bull's trench kiln

The kiln is fired continuously and has to be loaded with a constant number of bricks every day. This demands a good organization of the brick production, and the production cannot easily be adjusted to fluctuations in the brick market.

The firing crew needs long time experience. Its moveable chimneys have a short working life. The moveable chimneys' exhaust temperature is high, causing a less than optimum firing

condition and fuel economy.

Laborer are working at brick kiln near Larkana -Sukker road

Tax collectors say they’ll use utility bills to estimate sales, but kilns mostly use coal. By Z AliPublished: June 13, 2011

There are an 1,500 brick kilns in Sindh, with each employing around 100 to 125 labourers. According to the federal budget 2012, a 17% tax will be imposed on brick kilns. PHOTO: EXPRESS

HYDERABAD:

Now that brick kilns are no longer exempt from paying a sales tax, anyone who wants to build a house with this cheapest of materials will have to fork out more. For example, if you are building a 120-square-yard plot double-storey bungalow for Rs2 million, buying bricks will take up 5% of the cost. Before the tax exemption that would cost you at the most Rs100,000. If the 17% sales tax is added, it will cost you an estimated Rs117,000.

Small wonder then that kiln owners are worried that paying a tax may force them to cut back on production. For its part, the Centre expects to rake in an additional earning of Rs106 billion by re-imposing a tax on several items, including cement, concrete blocks and bricks. Kilns with less than Rs5 million sales annually will remain exempt.

“Bricks are the cheapest material when it comes to the quantity used in construction work. But once the GST is imposed, the prices will obviously go up,” said Farooq Chaudhry of the Sindh Brick Kiln Owners Association. He told The Express Tribune that 12×6 inch bricks cost between Rs6,500 and Rs7,000 for every 1,000 pieces while the cheapest and smallest bricks are sold for Rs3,100 to Rs3,300 per 1,000, excluding transport charges.

Tax evasion

It is not as if these businessmen don’t agree that ideally, every sector should pay taxes. Haji Yaqoob of the Hyderabad Chamber of Commerce and Industry taxation committee feels for example that this should happen. However, he points out that with inflation, the tax would affect the kilns as well as the construction industry.

“Tax evasion is rampant in Pakistan and the competence of tax collectors is just as questionable,” he observed. Yaqoob is of the view that monitoring the production and sales of bricks every-day will be difficult for tax collectors. “Keeping in mind the informal system of manufacturing and sales, tax evasion or even corruption can’t be ruled out.”

He demanded that the tax department come up with an effective mechanism if the tax is to be imposed.

For their part, the tax officials say they have a few collection methods in mind. “We can check their stocks at a given time and assess their value. The capacity of their machinery and the size of a kiln can also provide an estimate of production. Utility bills can also help estimate sales,” suggested Imtiaz Shaikh, who is the Tax of Inland Revenue Service’s additional controller.

Tax collection

However, Shaikh had no specific method of collecting the taxes. He proposed deputing staff at the kilns to monitor the sales, but considering the fact that there are around 1,500 in Sindh alone, it seems impossible. As Farooq Chaudhry of the kiln association pointed out, utility bills won’t be much of an indication considering that kilns use coal for energy.

Those opposed to the tax fear that kiln owners may forge records to showing an annual sale of less than Rs5 million to evade the tax, also there will be hardly any mechanism to ensure that the bricks sold were not inclusive of GST.

“So far no specific plan has been devised to collect the tax,” said an Inland Revenue Service official.

The tax will also affect builders and developers, as they will end up paying between two-and-a-half to three per cent more for construction supplies. “The component for bricks is around three per cent while that for cement varies between 12 and 15 per cent of the total material for construction,” explained project manager for Abdullah Builders and Developers, Afzal Khan.

The rate of construction, currently Rs1,200, will grow to around Rs1,400, he added. “This simply translates into additional expenses of Rs250,000 to Rs300,000 on a Rs10 million project.” There are an estimated 1,500 brick kilns in Sindh, with each employing around 100 to 125 labourers. The kiln owners have planned to lobby the government to retain the exemption. Sindh Brick Kiln Owners Association president Haji Behram Khan told The Express Tribune that owners from all over the country will meet in Islamabad on June 13. Parliamentarians are also expected to attend. They will ask them to drop the plan to re-impose the sales tax.

Published in The Express Tribune, June 13th, 2011.