High performance gas analyzers for
GasEye analyzers can be applied in several places in a power plant starting from a coal silo (CO measurement), through boiler optimization (CO+O2+CH4+H2O) to emission control (NO, NO2, NH3, SO2, SO3) and CEMS (HCl, NH3, HCHO, HF). Both in-situ as well as extractive analysis is possible.
Coal Silo (CO)
Coal mill inerting system (O2)
Inerting systems avoid dust explosions and smouldering fires in silos, coal mills and filter equipment by creating an inert atmosphere. In the case of abnormal levels of carbon monoxide (CO), oxygen or heat, the inerting process is initiated automatically through a process-control system. Constant and accurate monitoring of oxygen level is therefore essential. The gas mixture is flammable in a range of concentration known as the explosive or flammable range. The goal at all times is to reduce the limiting O2 concentration below the Lower Explosive Limit (LEL). The exact value of the LEL depends on the kind of coal that is used. The Oxygen concentration needs to be measured accurately and with a short response time.
Optimization of combustion (O2, CO, CH4, H2O)
Combustion is the conversion of primary chemical energy contained in the coal into heat through the process of oxidation at high temperatures. The oxygen required for the combustion is supplied as part of the combustion air that is fed to the process. In a perfect combustion the amount of oxygen supplied is just sufficient to burn all combustibles completely. In real combustion, however, an excess volume of oxygen (air) must be supplied due to insufficient mixing of fuel and oxygen. Too high oxygen content will cause increased NOx content and energy losses through dilution with cool air. Too low oxygen content will cause increased formation of CO. Therefore, the excess air value is an important parameter for an 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 today one of the largest application for TLS analyzers in the power industry and the technology is rapidly replacing the Zirconia Oxide probes used earlier. 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. Oxygen concentration and gas temperature can be measured simultaneously in the same gas volume from a set of selected absorption lines by analyzing the relative line strengths of the lines.
Simultaneous measurement of the O2 and the CO concentration in the combustion chamber is an effective way to control the air – to – fuel ratio and obtain balanced combustion. It can be shown that the CO concentration in the optimum balanced combustion is around 200 ppm irrespective of fuel types and devices. Outside that air-fuel ratio range the CO concentration increases rapidly. A real-time in-situ CO measurement will aid in the optimization and acts as a complement to the O2 measurement in order to obtain a stable balanced combustion.
Methane (CH4) monitoring is important in gas fired power plants to monitor operation and detect failures of the gas burners.
Upstream the denitrification stage (NO, NH3)
A direct measurement of the NO concentration before and after the denitrification stage offers a 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 exact dosage of NH3.
After denitrification, before electrostatic filter (NH3, NO)
As its conversion efficiency and buffer capability is high, the NH3 slip behind a SCR catalyst is normally very low, e.g. in the range of 1 ppm or below. An increase of the NH3 slip at constant process conditions is a precise indicator of a decrease in the catalyst’s activity. Together with acidic flue gas components, excess NH3 injected to 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.
A direct measurement of the NO concentration before and after the denitrification stage offers a direct supervision of the efficiency of the deNOx process.
Electrofilter protection (CO)
Electrostatic filters, used for trapping of dust particles by electrostatic attraction, are very common in coal-fired power plants. Because of the high field strength spontaneous discharges can occur in the electrostatic filters. It is important to prevent flue gases with an excess CO concentration to enter the filter, since 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 the filter is a key issue for safe filter operation. In case of excessively high CO concentrations close to the limit of explosion, a fast and automatic shut-down of the filter can be realized due to the fast response time of the GasEye analyzer.
De-sulfurization (SO2, SO3)
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 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 real-time, continuous measurement of SO2/SO3 in power plants to control the feed rate of the lime or lime stone has been a long discussed desire of the industry. SO3 forms in the boiler combustion chamber and within the SCR system by thermal and catalytic oxidation of SO2. Thermal oxidation occurs in the high temperature zones of the boiler while catalytic oxidation is supported by the presence of metals such as iron ore, platinum or and vanadium typically used as catalysts in the SCR. While vanadium in the SCR promotes the positive reaction of NOx removal from flue gas, it has the negative side effect of generating SO3. 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 subsequent ductwork through the formation of other acid gases such as H2SO4 and ammonium bisulfate (NH4HSO4).
According to the German 13. FEPL regulations, a number of flue gas components like O2, CO2, CO, NOx, SOx and HCl must be monitored continuously at the stack using approved analyzing equipment.
In 2005 a European standard, EN 14181 was introduced which provides a formal quality assurance procedure to be applied tom CEMS installations.
EN14181 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.