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Specific Energy Consumption for Firing – What it is and Why you should use it

Ananthakrishnan Ravi | Tuesday 4 September 2018

Brick kiln owners are familiar with the basic process of brick making: clay preparation, moulding, drying of green bricks, and, finally, firing.

Brick manufacturing is an energy intensive process, with most of the energy being consumed towards firing the bricks.  The last stage of brick making is firing, which converts green bricks from a loosely compacted blend of different minerals into a strong, hard, and stable product. It is the firing process that determines the properties of the fired brick, including the strength, porosity, hardness, making it an important step that concerns all brick makers.

Calculating the energy consumed to fire bricks is an important parameter used to measure a kiln’s performance. Most brick makers calculate their kiln’s energy performance by the number of tons of fuel used per lakh bricks. However, this is not the best way to measure energy performance.  In this context, Specific Energy Consumption, or SEC, is used to understand a kiln’s energy efficiency by measuring the amount of thermal energy used to produce 1 kg of fired brick. This depends on the type of clay, operation practices, and the efficiency of kiln technology.

As a brick kiln owner, if you find that your kiln has high SEC, you should plan to improve your operational practices at the kiln. You may also consider shifting to a more efficient kiln technology. Efficient firing technologies, such as Zigzag Kiln and Vertical Shaft Brick Kiln (VSBK), have lower Specific Energy Consumption in comparison to conventional technologies such as Clamp and Fixed Chimney Bull’s Trench Kiln (FCBTK).

The following table gives the typical SEC of a few types of brick kilns which were monitored in India.

Kiln Type	Range of Specific Energy Consumption (MJ/kg)
Fixed Chimney Bull’s Trench Kiln (FCBTK)	1.1 to 1.5
Zigzag Kiln	0.9 to 1.2
Vertical Shaft Brick Kiln (VSBK)	0.6 to 1.0
Clamp	1.5 to 4.0

 

For calculating SEC, one requires not only the weight of the fired products but also the Calorific Value (C.V.) and the quantities of all types of fuels used in the kiln.

Let us consider a case to see why SEC is a better calculation method. Suppose two brick kilns located in Patna, one an FCBTK and the other a Zigzag Kiln, reported that both of them consume 15 tons of coal per lakh bricks, and the weight of fired bricks of both is 3 kg per brick. If no further information is available, one may conclude that the energy performance of the two kilns is the same. But with added information that the type of coal used in the two kilns was not the same – FCBTK uses US coal (calorific value 6,500 kcal/kg) and Zigzag Kiln uses Assam coal (calorific value 5,800 kcal/kg), calculating SEC of the kilns we know that Zigzag Kiln has SEC of 1.22 MJ/kg, while FCBTK has SEC of 1.37 MJ/kg. This means Zigzag Kiln consumes less energy than FCBTK.

Let us look at another example. Kiln A located at Yamunanagar uses three fuels for firing bricks – US coal (10 tons per lakh bricks), firewood (3 tons per lakh bricks) and sawdust (3 tons per lakh bricks). Neighbouring Kiln B uses only US coal (14 tons per lakh bricks). Both are FCBTKs. Which kiln is more efficient? By calculating SEC of the kilns, we know that Kiln A has SEC of 1.23 MJ/kg, while Kiln B has SEC of 1.28 MJ/kg. This means Kiln A consumes less energy than Kiln B.

SEC gives you a more precise and realistic calculation of actual energy consumed by your kiln. SEC is a simple calculation, which can easily let brick kiln owners know their kiln’s energy consumption. BrickGuru has made the process easier by developing an online calculator to give you results in minutes.  Go ahead and calculate the SEC for your kiln.

To find out the SEC of your brick kiln, check out the SEC tool on the BrickGuru website today – https://brickguru.in/tool/calculator.

Before you start using the calculator, you should be ready with the following data for the season for which you wish to calculate the SEC –

1. No. of months you operated your kiln
2. How many types of bricks you produced
3. Weight of all the types of bricks in kg
4. Quantity of bricks produced of all the types (in tonnes)
5. How many types of fuels you used
6. Quantity of fuels used of all the types (in tonnes)
7. Cost of all fuels used (Rs/ tonne).

Ananthakrishnan Ravi

The writer is a Consultant at
Greentech Knowledge Solutions Pvt. Ltd. New Delhi