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BWF Envirotec

Reduced Emissions by Optimizing the Efficiency of Filter Bags

Tuesday, 04 March 2014


OFFINGEN (DE) - It is a fact that with NESHAP, the new environmental rules, life will be changing for almost all cement plant operators in the USA and perhaps also around the world. 

Environmental compliance issues may become tougher to achieve. As a first step this may also be an opportunity to look at fixing what you have instead of immediately planning on replacing the dust control units with more expensive equipment.

One way of improving existing dust control units is to operate the cement kiln and all associated equipment with optimized parameters - make the kiln dust control units function better in all aspects of their operation.

The importance of cleaning filter bags properly

Cleaning the fabric filter bags in a pulse-jet baghouse is a dust control function that does not occupy highest priority in the cement manufacturing process. Dust control units will not produce any cement clinker and therefore these issues are shifted to an area of lower management focus. However, sometimes these minor details have a significant effect on the overall performance of the entire cement clinker production line. Optimizing cleaning of the filter bags in dust control units for example will make kilns run smoother, provide potential for optimized production at lower cost and reduce emissions.

A new way to upgrade the performance of the filter bags

BWF Envirotec has been highly active providing a new service that detects the current performance of the pulse-jet dust control system. Using CFD (Computational Fluid Dynamics) technology and pressure/flow analysis, the efficiency of filter bag cleaning is being measured off-line and on-line. Probes that work based on the Prandtl principle are inserted into the filter bags (figure 1) measuring the actual cleaning pressure and gas velocity. Off-line measurements will detect the distribution of the cleaning air (example in figure 2). On-line measurements will detect whether the cleaning pressure and velocity are sufficient for bag cleaning by overcoming the operational process pressure. By means of its analytical approach, the measured values can be recorded with sampling rates of up to 2000 Hz. Even the smallest changes in the filter system can be reliably detected and detailed information is provided about the condition of the filter medium and the pulse-jet dust control unit. Figure 3 shows an example of four bags being measured simultaneously on-line. Only two of the bags receive sufficient cleaning air. For the other two bags (black and green color in the graph) the cleaning air pressure just overcomes the process pressure, but is not enough to remove all the dust from the filter bags.

CFD in practice

Based on this analysis of the CFD analysis results, the operator will be offered physical modifications that help to make bag cleaning more effective. This CFD analysis and modifications were performed at a large number of European plants. Figure 4 is an example of a comparison of the cleaning air distribution before and after the modifications. As can be seen, the distribution of the cleaning air in its original configuration is very poor. A significant improvement is observed after implementation of the modifications. Those modifications are site specific. However, depending on the results of the CFD analysis, the blow pipe may become the focal point. The design of the holes will be altered in a way that the cleaning air is being directed into the center of the venturi as well as the quantity of air for each bag will be the same. After those modifications are being made and an extended operating period a reduction in cleaning pressure may be possible. Post probe measurements are recommended to assist in each step of the improvements.

Significant improvement in bag service life

Although different from one plant to another, improvements in bag cleaning may often amount to more than 20%. In most cases, this would enable operators to reduce cleaning pressure, which will increase bag life. Maintaining the integrity of the filter bag over a longer period of time will subsequently reduce emissions. This may be sufficient in order to comply with the new NESHAP rules in the USA.