HISTORY
A biogas company consulted with Ship & Shore Environmental, Inc. (S&SE) to engineer a system to reduce emissions and abate volatile organic compounds (VOCs). This system was designed in order to reduce four streams high in nitrogen and sulfur while also reducing the production of NOx. The waste stream produces a large value of nitrogen gas, therefore the oxidation process in a standard Direct-Fired Thermal Oxidizer (DFTO) would produce an abundance of NOx gas.
SOLUTION
In order to combat the production of VOCs in the plant, the client hired Ship & Shore Environmental, Inc. (S&SE) to provide a design for a reliable system solution. S&SE engineers and technicians visited the site to observe and test the concentrations of VOCs emitted and measure the space available. After all the data was collected, the team reviewed it, and a recommendation was made to meet all the company’s concerns.
The recommended solution involved a custom state-of-the-art Multi-Stage Thermal Oxidizer installed downstream of a pyrolysis furnace and multiple condensers to thermally oxidize the waste streams high in sulfur and nitrogen concentration while also limiting the formation of nitrogen oxides (NOx). One unique aspect about the design of this system is that there is no direct ignition of the gas, and rather, the whole system is kept at auto ignition point. The Multi-Stage Thermal Oxidizer has two main processes (with three total stages). The initial stage is reducing; this happens in an oxygen-starved chamber operating at a temperature of 2150°F. A second reducing stage will also occur in the oxidizer or the second chamber, at a temperature of 1650°F. This is to assure that there is no excess NOx produced. The following stage is the cooldown process. The cooldown process has two outlets, one outlet that leads to the temperature exchange and the other that leads to the quencher. The heat exchanged can be used to heat the inlet temperature, or it can take heat to be used anywhere else in the plant.A unique challenge for biogas plant engineers was the limited space and potential for excess NOx with the stream having high nitrogen content. While the low-NOx Thermal Oxidizer is not designed for 100% destruction of NOx gas, it can stop the excess production of NOx.
Ship & Shore Environmental’s design was created vertically in order to fit within the designated area. This means that any production of ash was eliminated. Finally, another benefit to this system is the client will not have to use natural gas for combustion and there will be an excess of heat present that will then be usable in other parts of the plant. These two features of the system significantly lower the overall cost both upfront and in the long-term
