Buildings and Industry

Waste Hydrogen in Dryers at Chemical Plant

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Summary

Eka Chimie Canada Inc. in Québec, manufacturers of sodium chlorate used in the pulp and paper industry, have succeeded in reducing their plant's energy costs. The most recent energy efficiency project adopted by the company concerns using waste hydrogen from the manufacturing process as an energy source for drying the sodium chlorate. The company expects to reduce its annual electricity bill by CAD 225,000 through this project.

The Situation

To convert the dryers to burn hydrogen, each dryer was fitted with a direct-fired Maxtherm burner, also called an airflow burner. Although the flame temperature is very high, the length of the flame is quite small because of the considerable flow of air in the duct (10,000 m³ per hour) for about 1 MW of energy. Only a small amount of NO_x is produced. This type of burner, compact and simple in design, provides excellent performance, since combustion occurs within the stream of air to be heated. Therefore there are no energy losses related to heat exchange. For this project, the burners were installed directly into the drying air ducts, upstream from the electric heaters, which were kept as a backup system.

The hydrogen released by the electrolytic process is recovered and purified by a wet scrubber to remove the chlorine. It is then pressurised to 100 kPa by booster compressors and led to an activated carbon filter to eliminate residual organic contaminants. From there, the hydrogen is fed to the dryers, where it is regulated and injected into each burner for combustion. On contact with the flame, the process air is heated to the desired setpoint (130°C) and mixed with the water vapour resulting from hydrogen combustion. However, the amount of water vapour in the air is not enough to affect the performance of the dryers. As it leaves the burner, the pressurised hot air is directed to the fluidisation area of the dryer to dry the sodium chlorate. The moisture content of the chlorate is reduced from 2.5% to 0.02% during the drying process. The exhaust air leaving the dryer is then treated by an air purification system consisting of a cyclone separator and wet-type air washer. Figure 1 illustrates the process for manufacturing sodium chlorate.

When operating these systems, a number of steps must be taken to make the use of hydrogen as safe as possible. Hydrogen, like sodium chlorate, requires certain precautions, and plant employees are made aware of these safety aspects through a continuous training programme.

The Company

Eka Chimie Canada Inc. in Magog, Québec, Canada, is a division of the multinational Akzo Nobel Corporation. Since 1979, the plant has used an electrolytic process to produce sodium chlorate. The Magog plant, which has 80 employees, produces 150,000 metric tonnes of chlorate per year in accordance with the IS0 9002 standard and strict health and safety standards.

Economics

Eka Chimie Canada Inc. has invested CAD 300,000 to convert its dryers. In return, the expected annual energy savings are around CAD 225,000. The investment payback period is therefore approximately 1.3 years.