The coal is stored in large coal silos from where it is fed to a coal mill which converts the coal into a fine powder ready for combustion. A serious threat in the operation of coal silos is the accidental occurrence of partial coal self-ignition. This results in an elevated concentration of CO inside the head-space of the silo, creating a risk of explosions and toxic impacts. Self-ignition is difficult to predict because its occurrence depends on several parameters. An effective protective measure is to monitor the CO concentration in the head space of the silo. The GasEye cross-duct is installed to measure the CO concentration directly inside the coal silo just across the head space, allowing a very fast measurement response. Increased CO concentrations provide an early indication of a fire, enabling immediate, preventive countermeasures. A typical measurement range is between 0 – 5%, however the superior sensitivity and stability of the Airoptic GasEye cross-duct analyzer provides an excellent early detection and warning system with a low risk of false alarms.

Possible solutions:

CO analyzers

Inerting systems prevent dust explosions and smoldering fires in silos, coal mills, and filter equipment by creating an inert atmosphere. In the event of abnormal levels of carbon monoxide (CO), oxygen or heat, the inertization process is automatically initiated by the process control system. Therefore, constant and accurate monitoring of the oxygen level is essential. The gas mixture is flammable within a concentration range known as the explosive or flammable range. The goal at all times is to keep the O2 concentration limit below the Lower Explosive Limit (LEL). The exact LEL value depends on the type of coal used. The oxygen concentration must be measured accurately and with a short response time.

Possible solutions:

O2 analyzers

Combustion is the conversion of the primary chemical energy contained in coal into heat through the process of oxidation at high temperatures. The oxygen needed for the combustion is supplied as part of the combustion air that is fed to the process. In perfect combustion, the amount of oxygen supplied is just sufficient to burn all combustibles completely. However, in actual combustion, an excess volume of oxygen (air) has to be supplied due to insufficient mixing of fuel and oxygen. Too high oxygen content will cause increased the NOx content and energy losses through dilution with cool air. Too low oxygen content will result in increased formation of CO. Therefore, the value of excess air is an important parameter for the optimal combustion process and economic plant operation. In-situ measurements of the oxygen concentration directly in the hot combustion zone using a laser based analyzer such as the GasEye cross duct system, have proven to be very useful for optimization of the combustion process. This is also one of the largest application of TLS analyzers in the power industry today, and the technology is rapidly replacing the previously used Zirconia Oxide probes. User benefits include higher efficiency since less excess air has to be heated up leading to costs savings on electric power. Moreover, using a TLS analyzer the oxygen concentration and the gas temperature can be derived in real-time. The oxygen concentration and the gas temperature can be measured simultaneously in the same gas volume from a set of selected absorption lines by analyzing the relative line intensities. Simultaneous measurement of O2 and CO concentrations in the combustion chamber is an effective way to control the air – to – fuel ratio and achieve balanced combustion. It can be shown that the CO concentration in the optimum balanced combustion is around 200 ppm regardless of the type of fuel and devices. Outside this range of air-fuel ratios, the CO concentration increases rapidly. Real-time in-situ CO measurement will aid in the optimization and acts as a complement to the O2 measurement in order to achieve stable, balanced combustion. Methane (CH4) monitoring is important in gas-fired power plants to monitor operation and detect gas burner failures.

Possible solutions:

CO + O2 analyzers

CO + CH4 + O2 analyzers

CO + O2 + H2O + CH4 analyzers

Direct measurement of the NO concentration before and after the denitrification stage offers direct supervision of the efficiency of the deNOx process and control of the denitrification process.
Selective Catalytic Reduction (SCR) deNOx installations are common for large scale combustion plants like coal fired power utilities. Nitrogen oxides (NOx) formed in combustion processes are efficiently reduced to water and nitrogen in the SCR process. Ammonia (NH3) or urea (CO(NH2)) is introduced to the flue gases upstream of a heterogeneous catalyst where the reduction takes place. Depending on the amount of dust, type and concentration of acidic gas components in the flue gas, the SCR process is normally operated in the temperature range of 300 °C – 400 °C. One GasEye cross-duct sensor can be used to control the ammonia concentration in-situ directly after the high temperature reaction, enabling real-time control of the exact dosage of NH3.

Possible solutions:

NO analyzers

NH3 analyzers

NO + NH3 analyzers

As its conversion efficiency and buffer capability are high, the NH3 slip behind an SCR catalyst is normally very low, e.g., in the range of 1 ppm or below. The increase in NH3 slip under constant process conditions is a precise indicator of a decrease in the catalyst’s activity. Together with acidic flue gas components, excess NH3 injected into the flue gas can lead to salt formation, which causes corrosion and other difficulties in the process.
The GasEye cross duct NH3 offers a sensitive measure of the ammonia slip with a short response time. Direct measurement of the NO concentration before and after the denitrification stage enables direct supervision of the efficiency of the deNOx process.

Possible solutions:

NO analyzers

NH3 analyzers

NO + NH3 analyzers

Electrostatic filters, used for trapping dust particles by electrostatic attraction, are very common in coal-fired power plants. Because of the high field strength, spontaneous discharges may occur in the electrostatic filters. It is important to prevent flue gases with an excessive CO concentration from entering the filter as the gas is flammable and can be ignited by electric sparks. Therefore, fast and continuous monitoring of the CO content of the flue gas upstream of the filter is a key issue for the safe filter operation. In the event of excessively high CO concentrations, close to the limit of an explosion, a fast and automatic shut-down of the filter can be realized due to the fast response time of the GasEye analyzer.

Possible solutions:

CO analyzers

As sulfur dioxide is responsible for acid rain formation, strict regulations have been enacted in many countries to limit the amount of sulfur dioxide emitted from power plants and other industrial facilities. SO2 is an acidic gas, which is why the most common large-scale desulfurization method is wet scrubbing using an alkaline sorbent such as lime or limestone to neutralize and remove the SO2 from the flue gas (wet flue gas desulfurization). Since lime and limestone are not soluble in water, they are used either in the form of an aqueous slurry or in a dry, powdered form. In recent years, there has been an increased demand for continuous, real-time SO2/SO3 measurement in power plants to control the feed rate of the lime or lime stone, which has been a long-debated industrial desire. SO3 is formed in the boiler combustion chamber and in the SCR system by thermal and catalytic oxidation of SO2. Thermal oxidation takes place in the high temperature zones of the boiler, while catalytic oxidation is promoted by the presence of metals such as iron ore, platinum or vanadium, typically used as catalysts in the SCR. While the vanadium in the SCR promotes the positive reaction of NOx removal from flue gas, it has the negative side effect of generating SO3. The SO3 formation in the flue gas of a coal fired power plant is undesirable as it can lead to a higher corrosion potential in the air pre-heater and in the subsequent ductwork through the formation of other acid gases such as sulfuric acid (H2SO4) and ammonium bisulfate (NH4HSO4).

Possible solutions:

SO2 analyzers

SO3 analyzers

According to the German 13. FEPL regulation, a number of flue gas components such as O2, CO2, CO, NOx, SOx, and HCl must be monitored continuously at the stack using approved analyzing equipment.

In 2005, the European standard EN 14181 was introduced, which provides a formal quality assurance procedure to be applied to CEMS installations.

The EN14181 standard defines three Quality Assurance Levels – QAL1, QAL2 and QAL3 – and an Annual Surveillance Test (AST). In general, a QAL2 certification is required, which means regular in-situ calibration of the CEMs equipment.