Most Read
Most E-mailed
E-mail Article
Print ArticleOriented strand board manufacturer reduces operating costs with fuel injection system that cuts energy consumption
A major oriented strand board (OSB) manufacturer owned a regenerative thermal oxidation system (RTO) that processed the emissions from multiple rotary drum dryers. Its plant processed primarily hemlock and other northern species that are relatively "soft" woods. To reduce the natural gas and electrical consumption of the RTO, a supplemental fuel injection system manufactured by Dürr Environmental was added.
The company chose Dürr due in part to their having supplied the original RTO equipment.
In the rotary drum dryers, wood strands or wafers are dried with a large volume of direct fired hot air. The product is also conveyed through the dryer with this air. Dryer air is heated by a burner fueled with both natural gas and sawdust. In this drying process, VOCs such as pinenes and turpenes are released along with large volumes of water. The total volume of air utilized for dryer heating and conveying is sent to the RTO for oxidation. With relatively low VOC concentrations, supplemental fuel (natural gas or propane in the winter) and electrical costs to operate large fans are a primary concern. An additional concern is the formation of Nox from the combustion of natural gas and propane at high temperatures in the RTO.
Dürr Environmental’s supplemental fuel injection system was designed with a sparger pipe located in the inlet air duct, a modulating control valve and a supplemental valve shut off train. After the RTO has been preheated to operating temperature and operating online with the process, the burners and combustion air blowers in the RTO combustion chamber are shut off.
The natural gas required to maintain combustion temperature is then injected into the inlet air stream via the sparger pipe. The maximum volume of gas injection is limited to less than 25 percent of the L.E.L. by sparger pipe sizing and flow control orifice plates.
The direct injection of natural gas into the air stream results in lower overall fuel consumption because the cold outside air (combustion air), for the burners is no longer required. Electrical consumption is reduced because the volume of air handled by the fan is now lower (no supplemental combustion air) and the air temperature is also lower. Nox emissions from the RTO are also dramatically reduced because the combustion of the injected natural gas takes place at a temperature below the temperature required to produce combustion created Nox.
