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Thinking ahead pays
Buyers of dust and fume extraction equipment often only consult manufacturers of such equipment when the machinery it is needed to operate with has already been installed. This is a frequently made mistake, writes Andy Quail, Chief executive of J B Thorne. It can lead to reduced performance, inefficient extraction and increased costs.
Dust extraction is often seen as an expensive addition to important production equipment. With no overt financial return, it can become an unnecessary irritant between management and employees, thought to cause loss of production and to take up vital resources. However, with increasingly stringent legal health and safety requirements coming into force, dust and fume extraction equipment is no longer a peripheral, bolt-on factor. Now it is essential to consider the risk of dust generation at an early stage when designing machinery or purchasing process equipment. In turn, this can make a huge contribution to added value, by reducing plant costs, and improving working conditions, product quality and presentation.
When designing processes or machinery, careful selection of the material to be handled or its treatment to reduce the generation of dust or time is an essential first step. A thorough analysis of the proposed operation and their sequence toward the reduction of the generation of dust particles, or the possible production of larger particles, can often result in reduced costs. Unfortunately it is extremely difficult to eliminate dust generation completely though there are a number of options for reducing and collecting the dust generated through suppression, total enclosure or partial enclosure. The choice of approach will depend on the process being planned.
Suppression
Dust suppression will depend on the type of work being carried out, and the effect of the suppressant on the dust and its application. This type of solution will be considered in light of the end use of the products and the effect of any liquid used in this process.
Total Enclosure
Total enclosure is often impractical, and dust trapped in the enclosure will need to be removed before maintenance can be carried out. There is also the risk of explosion, damage and wear on bearing surfaces, and the risk of product contamination. It is difficult to seal an enclosure and some means of overcoming the pressure build up within the arrangement must be found. This may be achieved by inducting a small negative pressure generated by a dust collector. However, this may lead to high concentrations of dust within the product.
Partial enclosure
The most common approach is the partial enclosure - either receptor or capture hood. The receptor hood is designed to receive the dust particles as they are generated. This is a cost effective system requiring mush less air and therefore, a smaller dust collection plant. A capture hood requires more air to draw the dust onto the system and as a consequence the size of extraction equipment is increased.
Plant and Equipment
It is essential that the filter size and efficiency is compatible with the hooding design and operation, or the system will not function efficiently.
Selection of an appropriate dust or fume filter will depend on the amount size and condition of dust captured by the hooding arrangement. This should be considered with the amount of air being drawn into the system. These factors will determine the type of filtration and efficiency levels that need to be achieved to meet legal and operator obligations.
A major influence on the filter selection will be the type of operation being carried out and the duration of the operating cycle. This will determine whether the extraction system must cope with continuous or intermittent operation. Once these considerations have been solved, attention must be given to re-using or recovering the waste product; this could help recover the cost of the dust extraction plant. If this is not possible, alternative uses should be sought, for example, the possibility of selling the waste product on.
It is important that dust and fume extraction systems are kept under negative pressure until the air is cleaned. This will prevent the dust escape and improve overall system efficiency. No amount of sophistication in filter material unit design, will give an optimum solution unless consideration is given to the specific application, and to the type and design of the hooding.
Understandingly all aspects of the operation that is generating the dust, the type of dust to be removed, and the level of performance that may be achieved is vitally important. Proper application of the dust extraction unit should then eliminate unnecessary costs and customer disappointment because of a shortfall on performance.
Once a system is installed, regular service and maintenance is essential to sustain design performances. Changes in the dust-generating operations being served require re-consideration of the dust control system and the resulting effects in the extraction equipment. By simply adding connections to an existing system the efficiency of a previously well-balanced system can be destroyed. If additions or changes are planned, the system should be re-assessed and if necessary, re-designed.
Correctly designed dust extraction equipment will help companies to meet their legal and moral obligations to their employees, protecting them from current or future hazards. Secondly, hazards such as moving and disposing of collected dust are an equally important consideration. Any added value to the product will depend on the requirement of the customer and industry sector involved, but in many cases it is a big advantage to be able to sell a "dust free" product.
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