Companies are increasingly exploring alternatives to fossil fuels, due to their high prices and stricter government regulations. Simply venting or flaring process by-products to the atmosphere no longer meets industries’ environmental and energy trends, and there are a number of innovative solutions that companies have successfully implemented to improve their energy and environmental performance. Among these solutions is the combustion of alternative fuels, such as biogas refinery fuels, hydrogen and flammable liquids, to produce usable power.
Motivation to make a change
Behind each alternative fuels project is an incentive that justifies the additional investment and development costs. In most cases, the motivation involves two factors: environmental regulations and/or energy cost savings.
The disposal of process by-products can be problematic when considering the cost of transport or post-treatment. In some cases, there are no alternatives available due to strict emission regulations preventing the venting or removal of certain gases
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How can combustion be a solution to emissions concerns when it is also a source of pollutant emissions? Today, modern combustion systems can be designed to be clean burning and extremely efficient. With the latest burner designs and combustion control technologies, emissions of NOx, CO, VOCs and particulate matter can be maintained below the local regulation limits. Typically, when firing low-BTU alternative fuels, NOx emissions are not an issue since they inherently burn “cooler” than conventional fossil fuels. CO and VOCs emissions, on the other hand, must be carefully controlled by designing the system so that furnace temperatures are kept at adequate levels for proper oxidation.
The combustion process also will oxidize the combustible chemical compounds that are contained in the waste stream and are potentially harmful to the environment. This category includes VOCs, THC and aromatics such as benzene. Proper design of the combustion system will provide the necessary conditions for the complete oxidation of those compounds into CO2 and water.
In addition, waste streams can contain inert matter or elements that the combustion cannot oxidize into harmless gases. These include sulphur (responsible for SOx emissions), fuel bound nitrogen (that will increase NOx emissions) and other elements (like metals of minerals that will be responsible for particulates emissions). Special attention must be given to the solids contained in the fuel that can degrade the combustion chamber or boiler tubes. Chemical analysis of process fuels is necessary to determine the concentration of such elements and compounds. A case-by-case evaluation is necessary to predict performance of waste stream combustion. Some examples of waste streams are: digester gas, landfill gas, off-gas, tail gas, dryer exhaust gas, fatty acids and tars.
Comparison between the cost of the combustion alternative and the other disposal solutions will determine which remedy will be the most profitable. The evaluation must analyze the potential energy value that can be present in some waste streams. With respect to the capitalization cost, it is possible to modify an existing combustion unit. Other times it is necessary to install a new system.
Alternative fuels yield cost savings
The cost of energy typically has a significant impact on a company’s bottom line due to an upward price trend in conventional fossils fuels. Most long-term forecasts predict this trend will continue with the growing global demand and limited supply of resources. Therefore, process flow charts are being scrutinized to determine if any by-product might contain sufficient energy that can be used as an alternate source.
