Coal is the basic fuel in conventional brick firing. Approximately 65% of brick production cost through traditional technologies is attributed to energy costs. The energy comes from using external fuel (i.e., coal) and internal fuel (e.g., boiler ash, sponge iron waste) in the green bricks. Although coal is the only type of external fuel used in the traditional brick firing technologies, there are sporadic instances of using mustard husk, biomass briquettes and wood as some alternates.

The Taragram-Datia EcoKiln operated by Tara Nirman Kendra uses coal and sponge iron waste as internal fuel sourced from Bhilai, Chattisgarh. Within a year, coal prices increased from Rs. 2500 per ton to Rs. 3200 per ton, affecting the cost of brick production. With no respite in the near future, coal prices are slated to increase considerably. Management and quality problems also occur in procuring coal from such a distance, jeopardizing consistent productivity and profitability.

To ensure profitability in brick production and ensure as a reliable and continuous supply of external fuel, a search for alternative fuels was initiated. Going by the past of using char pellets, it was the only feasible option selected. The various advantages of char pellets envisaged were:

n  Potential to create new enterprises

n  Ability to be produced locally, thus reducing dependency on external supply sources

During the period 29 December 2006 to 15 January 2007, a pilot trial was conducted at the Datia EcoKiln. The primary objective was to test the efficiency of pellets under production scale conditions. A brief summary of comparative results is given in the table below.

Although the application results were acceptable, major problems occurred with the quality of pellets. The composition used for making the pellets was biomass char and 10% by weight plastic fire clay. With usual ageing for soil, the pellets were fabricated in the Pelletizer machine supplied by M/S Sandhya Engineering Pvt. Ltd. However, the pellets did not achieve the required solidification. Fully dried pellets had a breakage of approximately 50% during local transportation within the production yard. During firing, these broken pellets (in the form of coarse dust) choked the airflow gaps between green bricks and melted. The high percentage of broken pellets was also not economical in brick production.

The primary objectives of the study, commissioned by the India Canada Environment Facility project were to:

n  Finalize the composition of char pellets

n  Prepare good quality pellets for commercial production

n  Demonstrate of pellets as an alternate fuel, replacing coal

In order to increase densification, coal dust powder and sponge iron waste powder here used partially, replacing char. Both sponge iron waste and coal powder possess higher specific gravity and aid in achieving the required density. Also, these two materials have appreciable calorific value to supplement the heat value of the char when partially replaced. Bentonite was selected as the binder for making char pellets due to its high plasticity. It was mixed in ratios of 5, 10 and 15%. Higher percentages were not added since it would increase the ash content and decrease the heat value. To prepare pellets, char was procured in the powdered form. It should be mentioned that the char was not sieved in a fine mesh. Coarse particles were deliberately retained so as to achieve greater densification. All the compositions were mixed in dry conditions and watered. Ageing was done for 12 hours. Pellets were made using the Sandhya Engineering machine.

The raw materials were tested for calorific value along with the final pellets of different compositions. Solidification tests were carried out adopting the drop ball method.

Results of Calorfie Value tests of raw materials used are :

1. Coal being used for brick production 3198 KCal/kg

2. Biomass char 4218 KCal/kg

3. Coal dust from TNK production 3297 KCal/kg

4. Sponge iron waste 2167 KCal/kg

Based on the above results, it can be seen that the heat value of pellets made with coal dust are higher than that of sponge iron waste compositions. This is due to the lower heat

value of the sponge iron waste. With increasing percentage of bentonite addition as a binder, the resistance to impact loads of pellets increases. However, the heat value decreases due to the increased addition of inert materials, which do not contribute to the heat content of the pellets. Also, pellets made with 5% bentonite have reasonable strength.

Here, the report will only give a comparative view on the material cost for the pellets. The material costing of the pellets has been done on the basis of the following cost assumptions:

n Char                Rs. 2000 per tonne

n  Sponge iron      Rs. 1470 per waste tonne (as on April 2007)

n  Coal dust         Rs. 3100 per tonne (as on April 2007)

n  Bentonite         Rs. 2500 per tonne

Material cost of the various pellet compositions are given below. In this calculation process, wastage of 5% during storage and handling of materials has also been included. Packing charges have not been included since they will be reusable.

n  Only char compositions

    - Composition A1        Rs. 2153 per tonne

    - Composition A2        Rs. 2174 per tonne

n  Sponge Iron waste-based compositions

    - Composition B1       Rs. 1971 per tonne

    - Composition B2       Rs. 2001 per tonne

    - Composition B3      Rs. 2028 per tonne

n  Coal dust-based composition

    - Composition C1     Rs. 2461 per tonne

    - Composition C2     Rs. 2469 per tonne

    - Composition C3     Rs. 2476 per tonne

It should be noted here that the costing

will vary with variation in the procurement prices of raw materials. The coal dust cost has been taken as the actual coal cost since it is presumed to be taken from EcoKiln production sources only.

Based on the calorific value and the field strength tests, it is recommended to use the following composition for brick production.

Composition code C1

Biomass char                                70

Coal dust (sieved in 3 mm mesh)    30

Bentonite                                      5% by total
(powdered form)                             weight of
                                                    principal raw
                                                    materials

Procurement of raw materials

Sieving of additives (3mm mesh)

Batching and proportioning

Raw materials mixing in dry stage

Watering (20 to 25%) and ageing for at least 12 hrs

Fabrication of pellets

Collection of good shape and size pellet

Drying in hard surface

Packing

Dispatch

It is recommended to fire bricks using pellets in a dual fuel mode. The pellets should be used between 50-60% by weight and coal 50-40% by weight. One should always use solid pellets and not the dust from the pellets. These pellets are reusable.

n  Additives, e.g., sponge iron waste and coal dust should always be sieved.

n   Bentonite should be used in powdered form.

n  All raw materials must be mixed homogenously. Use of Muller Mixer for the above process is recommended during production scale.

n  The mix should be aged in water for a minimum period of 12 days in a moist condition. Care should be taken that the water does not evaporate.

n   Water should be used between 20%-25%.

n   Clean the Pelletizer roller before daily production.

n   Rollers should be tightened before commencing work. q

Nandan Santra