An odor predictive model for Rendering applications

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Abstract
The rendering process consists of crushing and heating animal remains to produce by-products. The U.S. produces approximately 30 billion pounds of inedible animal by-products annually, exporting a market value of US$ 1.5 billion. Benefits of the rendering process include reducing total waste material, and helping the livestock industry stay competitive over vegetable protein manufacturers. However, the rendering process can have a negative effect on the environment through the emission of nuisance odorous compounds such as hydrogen sulfide, reduced sulfur compounds, ammonia, various fatty acids, ketones and aldehydes. Several strategies are currently used to combat odor in rendering facilities. In recent years, rendering facilities are increasingly selecting biofiltration for combating nuisance odor. This work describes modeling and design strategies used in building large-scale biofilter systems of up to 250,000 cfm (cubic feet per minute) capacity. The models facilitated in the design and evaluation of operating conditions and capital investment. This work demonstrates that models play an important role in the design of large-scale odor control systems that deliver predicted performance.

1. Introduction
The rendering process consists of crushing and heating animal remains to remove moisture, thereby allowing the fat to be separated from the high-protein greaves. These greaves are then ground into bone meal, a livestock feed with good market value and high nutritional value. Fat, a major byproduct, is used in cooking, frying, soap, detergent, candles, deodorants, paints, cosmetics, shaving cream and caulking compounds [1—2]. Other by-products of the rendering process are used in pharmaceuticals, leather, glue and fertilizer. The rendering market is large and according to Ockerman and Hansen [1], the U.S. produces approximately 30 billion pounds of inedible animal by-products annually, exporting a market value of US$ 1.5 billion. Benefits of the rendering process include reducing total waste materials and helping the livestock industry to stay competitive over vegetable protein manufacturers [1]. However, rendering can have a negative effect on the environment through the emission of nuisance odorous compounds into the atmosphere from the process fa-cilities. The most odorous section of a rendering plant is the blood storage area. Odors from this area result from amino acids and peptides present in blood. Other foul-smelling areas are the singeing ovens, the gut department and the wastewater treatment facility [2]. The combustion of fossil fuels in ovens during the heating process also creates air pollution in the form of SOA, NOA and carbon dioxide. Additionally, at high temperatures, by-products of fat and protein breakdown become volatile and are typically odorous. Chemical by-products include hydrogen sulfide, ammonia, various fatty acids, ketones and aldehydes (refer Table 1).

Government regulations on odor emissions and air quality standards help monitor and control excessive emissions from plant facilities. In the United States, there are no federal odor regulations approved by the Environmental Protection Agency (EPA). Instead, odor emissions are monitored at the state and municipal levels [3]. In Canada, odor issues are dealt with at the provincial level, and odor is quantified based on emission rates and off-property boundary odor levels. Several strategies are currently used to combat odor in rendering facilities. The first step is to reduce odor at its source. This involves limiting the storage of raw materials (i.e. animal remains), maintaining cool temperatures, pasteurization to retard decomposition and general plant cleanliness. However, the above techniques are limited in their effectiveness, a secondary treatment must often follow, conventionally being adsorption, incineration or chemical scrubbing. Adsorption using carbon filtration is effective for low concentrations of contaminants, but problems arise when the adsorption bed reaches its adsorption capacity and must be disposed of at significant expense. Thermal and catalytic incineration are commonly used methods that involve combustion of odorous compounds at high temperatures; these processes are only feasible at moderate to high pollutant concentrations, and use a non-renewable petroleum-based fuel source. Chemical scrubbing uses the principle of pollutant oxidation to produce relatively odorless and harmless products. However, complex operational controls and intrusive chemicals requirements make operating costs very high.

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