Siemens Industry, Inc. - Process Analytics

Electrofilter protection by fast monitoring of CO in flue gas – Case Study


Electrostatic precipitators

Many industrial operations produce exhaust gases that contain dust, fly ash (unburned constituents), fumes (including fine elemental particles such as cadmium, sulfur and lead) and mist (such as coal tar), which cause an unwanted impact to human health and the environment. One widely used method of removing such contaminants from a gas stream is to use an electrostatic precipitator (ESP).

Basically, in an electrostatic precipitator the flue gas is sent through pipes having negatively charged plates which give the particles a negative charge. The particles are then routed past positively charged plates or grounded plates, which attract the negatively-charged particles. The particles stick to the positive plates until they are collected. Provisions must be taken to avoid flammable gases to enter the filter, since the gas could be ignited by sparcs occuring between the electrodes.

Electrostatic precipitators are used in power applications as well as in other industries such as cement, pulp & paper, petrochemicals and steel.

Fast and continuous monitoring of the CO concentration in flue gases upstream an electrostatic filter is a key issue for safe filter operation because it prevents the filter from the danger of explosion caused by too high CO concentration.

The in-situ measuring principle is best suited for this task because it provides measuring data in realtime for immediate reaction. The LDS 6 in-situ Laser Gas Analyzer offers all capabilities for this application. Installed upstream the filter, it delivers fast and accurate CO concentration data that can be further processed in a saftety control circuit.

This Case Study presents details of this application.

Application tasks

Particle emitting processes like cement manufacturing and waste incineration are using electrostatic precipitators (ESP, electro filter) to trap and eliminate solids in the flue gas. Within the same processes, CO can sometimes occur at critical levels.

If the presence of CO in the electro filters exceeds a certain level (normally around 10%), electric sparks can provoke hazardous explosions and thus lead to an immediate shut down of the filter operation.

Any filter shut down leads to unfiltered emissions and to contaminations of the plant surroundings. Moreover, the number of allowed filter shut-downs per year is often limited by legislative regulations and is constantly lowered. Avoiding too many filter shut-downs consequently secures compliance with the regulations as well as prevents forced production shut downs, which come along with significant financial losses.

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