COAL BOILER

Classification of coal quality are generally divided into two, namely the division in this scientifically based pembatubaraaan level, and the division based on the intended use.Based on sequence pembatubaraannya, coal is divided into a young coal (brown coal or lignite), sub-bituminous, bituminous, and anthracite. While based on the intended use, divided into coal steam coal (steam coal), coal coke (coking coal or metallurgical coal), and anthracite.Steam coal is coal which use the most extensive scale.

Based on the method, be using steam coal consist of direct utilization of coal that meets certain specifications used immediately after going through the process of crushing (crushing / milling) as the first coal power plant, then use the first process to facilitate handling (handling) such as CWM (Coal Water Slurry), COM (Coal Oil Mixture), and CCS (Coal Cartridge System), and then pemanfataan through a conversion process such as gasification and liquefaction of coalIn the coal power plant, the fuel used is coal steam which consists of sub-bituminous and bituminous class. Lignite also started to get a place as a fuel in power plant lately, along with the development of technology that can accommodate the generation of low-quality coal.

Figure 1. Electric generation scheme on coal power plant

(Source: The Coal Resource, 2004)

At the power plant, coal is burned in the boiler produces heat which is used to change the water in the pipe that is passed in the boiler into steam, which then is used to drive turbines and generators rotate. Electricity generation in power plant performance is largely determined by the thermal efficiency in coal combustion process, because in addition to an effect on the efficiency of generation, can also lower the cost of generation. Then in terms of environment, it is known that the amount of CO2 emissions per unit of calories from coal is the highest when compared with other fossil fuels, with a comparison to coal, oil, and gas is 5:4:3. So based on trials that get the results that the increase in thermal efficiency by 1% will be able to reduce CO2 emissions by 2.5%, then the thermal efficiency will be improved significantly reduce the environmental burden caused by burning coal.Therefore, it can be said that the combustion technology (combustion technology) is a major theme in the effort to increase coal utilization efficiency is directly at the same time anticipating the future environmental issues.Basically the method of burning the plant is divided into three, namely the burning of a layer of fixed (fixed bed combustion), the burning of coal powder (pulverized coal combustion / PCC), and the burning of a floating layer (fluidized bed combustion / FBC). Figure 3 below shows the type - the type of boiler used for each - each combustion method.Figure 2. A typical boiler by combustion method(Source: Idemitsu Kosan Co.., Ltd.)Combustion Layer FixedCoating method still uses stoker boiler for combustion processes. As the fuel is coal with ash content that is not too low and the maximum size of about 30mm. In addition, because of the limitation of coal grain size distribution is used, it is necessary to reduce the amount of fine coal that come mixed into coal. The reason does not use coal with ash content is too low is because the method of this combustion, coal is burned on top of a thick ash layer formed on the lattice of fire (fire traveling grate) in stoker boilers. If levels of very little ash, ash layer will not be formed on the lattice so that combustion will occur directly on the lattice, which can cause severe damage in that section. Therefore, the ash content of coal is preferred for this type of boiler is about 10-15%. The minimum thick layer of ash that is needed for combustion is 5cm.Figure 3. Stoker Boiler(Source: Idemitsu Kosan Co.., Ltd.)In this stoker combustion, ash from burning of small amounts of fly ash, only about 30% of the total. Then with an effort such as the burning of two levels of NOx, NOx levels can be lowered to about 250-300 ppm. Meanwhile, to reduce SOx, still needed additional facilities such as flue gas desulfurization equipment.Combustion of Coal Powder (Pulverized Coal Combustion / PCC)Today, most especially the large-capacity power plant is still using the PCC method on the combustion of fuel. This is because the PCC system is a proven technology and has a high level of reliability. Efforts to improve plant performance is mainly done by increasing the temperature and pressure of the steam produced during the combustion process.Development starts from the sub-critical steam, then super-critical steam, steam and ultra super critical (USC). As an example of USC power plant which uses technology is generating no. 1 and 2 belong to J-Power in Tachibana Bay, Japan, which boilernya respectively - each with a capacity of 1050 MW Babcock made by Hitachi. The resulting vapor pressure is 25 MPa (254.93 kgf/cm2) and the temperature reached 600 ℃ / 610 ℃ (1 stage reheat cycles). The development of steam conditions and graph generation efficiency improvement at PCC is shown in figure 4 in below.Figure 4. The development of steam power plant conditions(Source: Clean Coal Technologies in Japan, 2005)At PCC, crushed coal by using coal PULVERIZER used (coal mill) up to a 200 mesh (74μm diameter), and then together - the same with the combustion air is sprayed into the boiler to be burned. Combustion method is sensitive to the quality of coal being used, especially the nature ketergerusan (grindability), slagging properties, properties fauling, and water content (moisture content). Coal is preferred for PCC boilers that have properties ketergerusan with HGI (Hardgrove Grindability Index) above 40 and the water content of less than 30%, and the ratio of fuel (fuel ratio) is less than 2. Combustion with the PCC method will produce ash which consists itself of clinker ash as much as 15% and the rest of the fly ash.Figure 5. PCC Boiler(Source: Idemitsu Kosan Co.., Ltd.)...

When done burning, nitrogen compounds present in coal will oxidize to form the so-called fuel NOx NOx, whereas nitrogen in the combustion air will oxidize to form NOx too high temperature is called thermal NOx. In total NOx emissions in flue gas, fuel NOx content reaches 80-90%. To overcome this NOx, denitrasi action (de-NOx) in the boiler during the combustion process takes place, by utilizing the properties of NOx reduction in coal.Figure 6. Denitrasi process in PCC boilers(Source: Coal Science Handbook, 2005)In the combustion process, the speed of injection of coal powder and air mixture into the boiler is reduced so that the ignition and combustion of fuel also slows. It can lower the combustion temperature, which resulted in decreased levels of thermal NOx.In addition, as shown in Figure 6 above, the fuel is not all feed into the main combustion zone, but some included in the section on the upper main burner. NOx is produced from primary pembakara subsequently burned through 2 levels. In the reduction zone which is a first-degree arson or arson is also called reduction (reducing combustion), nitrogen content in the fuel is converted to N2. Next, do a second degree burning or combustion oxidation (oxidizing combustion), the form of complete combustion in the combustion zone. With this action, NOx in exhaust gas can be compressed up to 150-200 ppm. As for the desulfurization still requires additional equipment ie flue gas desulfurization equipment.Floating layer combustion (Fluidized Bed Combustion / FBC)In the combustion method FBC, coal crushed first by using the maximum-sized crusher to 25mm. Unlike combustion using coal stoker who put on the lattice heat during combustion or spray PCC method of coal and air mixture during combustion, coal grains kept in a floating position, by passing a certain wind speed from the bottom of the boiler. The balance between the upward push of the wind and gravity will keep the grains of coal remain in the floating position so as to form a layer of a fluid is always moving. This condition will cause the fuel combustion is more perfect because of the position of coal is always changing so that air circulation can be run properly and sufficient for the combustion process.Due to the nature of such combustion, the fuel specification requirements that will be used for the FBC is not as restrictive as in other combustion methods. In general, there are no special restrictions for levels of fly substances (volatile matter), the ratio of fuel (fuel ratio) and ash content. In fact all kinds, including low rank coal can be burned with either though using the method of this FBC. Only when the coal will be incorporated into the boiler, the water content attached to the surface (free moisture) are expected to not more than 4%. In addition to the above advantages, the value added of the FBC method is a tool used coal crusher is not too complicated, and the size of the boiler can be reduced and made compact.When the combustion temperature in the PCC is around 1400 - 1500 ℃, then the FBC, the combustion temperature range between 850-900 ℃ course so that the levels of thermal NOx that arise can be suppressed. In addition, the mechanism of combustion of 2 levels as in the PCC, the total NOx levels can be reduced again.Then, when the desulfurization equipment is still required for the handling of SOx in combustion method fixed and PCC, then at FBC, desulfurization can occur simultaneously with the combustion process in boilers. This is done by mixing limestone (lime stone, CaCO3) and the coal then simultaneously inserted into the boiler. SOx produced during the combustion process, will react with lime to form gypsum (calcium sulfate). In addition to the desulfurization process, limestone also serves as a medium for the fluidized bed due to its software so that the pipe heater (heat exchanger tubes) is installed in the boiler is not easy to wear.Figure 7. A typical FBC boiler(Source: Coal Science Handbook, 2005)Based on the working mechanism of combustion, the method is divided into two namely Bubbling FBC FBC and circulating FBC (CFBC), as shown in Figure 7 above. It could be argued that the Bubbling FBC FBC is a basic principle, while the CFBC is development.In CFBC, there is another tool installed on a boiler is a high temperature cyclone. Fluidized bed of media particles that have not reacted and unburned coal which flew with the flow of exhaust gas will be separated in the cyclone is then channeled back to the boiler. Through this circulation process, fluidized bed height can be maintained, denitrasi process may take more optimal, and higher combustion efficiency can be achieved. Therefore, in addition to low-quality coal, materials such as biomass, sludge, plastics, and scrap tires can also be used as fuel in the CFBC. The ash residue almost entirely of fly ash with the flue gas flow, and will be arrested first by using the Electric Precipitator before the flue gas exit to the chimney (stack).Figure 8. CFBC Boiler(Source: Idemitsu Kosan Co.., Ltd.)At FBC, when the pressure inside the boiler the same as the outside air pressure, called the Atmospheric FBC (AFBC), whereas when the pressure is higher than the outside air pressure, about 1 MPa, called the pressurized FBC (PFBC).Combustion air pressure factors influence the development of this FBC technology. To Bubbling FBC develops from PFBC to Advanced PFBC (A-PFBC), while for CFBC thereafter developed into the Internal CFBC (ICFBC) and then pressurized ICFBC (PICFBC).PFBCIn PFBC, in addition to the heat generated is used to heat water into steam to turn a steam turbine, combustion gas is also produced which has a high pressure gas turbine that can play, so that using a PFBC power plant generation has a better efficiency compared to AFBC due to a combination of mechanisms (combined cycle) is. Gross value generation efficiency (gross efficiency) can reach 43%.In accordance with the principles of combustion in FBC, SOx produced at PFBC can be suppressed by the mechanism of desulfurization along with combustion in the boiler, while the NOx can be suppressed by combustion at relatively low temperatures (about 860 ℃) and the burning of 2 levels. Because the gases of combustion are used again by running into the gas turbine, the combustion ash that come flowing out along with the gas needs to be removed first. Use CTF (Ceramic Tube Filter) can effectively capture these ashes.Pressurized condition that produces a better combustion will automatically reduce levels of CO2 emissions so as to reduce the environmental burden.Figure 9. Working principle of PFBC(Source: Coal Note, 2001)To further improve thermal efficiency, gasification unit partially (partial gasifier), which uses gasification technology floating layer (fluidized bed gasification) was then added to the PFBC unit. With the combination of gasification technology is the effort to increase the temperature of the gas at the entrance (inlet) gas turbine allows it to be done.In the process of partial gasification in the gasifier, the carbon conversion is achieved is about 85%. This value can be increased to 100% through a combination with the oxidizing agent (oxidizer). Further development of PFBC is called the Advanced PFBC (A-PFBC), the working principle is shown in Figure 10 below. Efficiency of net generation (net efficiency) which produced the A-PFBC is very high, can reach 46%.Figure 10. The working principle of A-PFBC(Source: Coal Science Handbook, 2005)ICFBCSectional boilers ICFBC shown in figure 11 below.Figure 11. Sectional boilers ICFBC(Source: Coal Note, 2001)As shown in the figure, the main combustion chamber (primary combustion chamber) and the decision space heat (heat recovery chamber) separated by a barrier wall mounted sideways. Then, because the pipe heater (heat exchange tube) is not attached directly to the main combustion chamber, then no worries about wear and tear of the pipe so that the silica sand is used instead of limestone for FBC media. Limestone is still being used as a reducing agent, SOx, only the numbers pressed in accordance with the purposes only.At the bottom of the main combustion chamber windbox attached to the wind flow to the boiler, where the small-volume air flows through the middle to create the layer moves (moving bed) is weak, and large-volume air flow through both sides of the windbox is to create a strong layer moves. Thus, in the middle of the main combustion chamber will form a layer moves down slowly, while on both sides of the room, the media will be lifted FBC strong upward toward the center of the main combustion chamber and then come down slowly - land, and then raised again by the large volume of the windbox wind. This process will create a spiral flow (spiral flow) that occurs continuously in the main combustion chamber. The mechanism of spiral flow of media FBC can keep floating layer so that a uniform temperature. In addition, because the flow is moving at a very dynamic, the disposal of unburnt material is also easier.Then, when the media is a powerful FBC raised up at the top of the barrier wall, some will be turned toward the heat collection chamber. Because the space is also taking a hot air flow from the bottom, then the space will be formed layers move down slowly as well. As a result, the media FBC will flow from the main combustion chamber leading to the capture chamber heat and then back again into the main combustion chamber, forming a circulation flow (circulating flow) between the two spaces. Using a heating pipe installed in the room taking the heat, the heat from the primary combustion chamber flows through the mechanism of circulation taken earlier.In general, changes in the volume of air supplied to the heat collection chamber is directly proportional to the coefficient of thermal conductivity as a whole. Thus it is only by setting the volume of the wind, heat and temperature levels keterambilan on floating layer can be well controlled, so that the load settings can be done easily as well.To further improve the performance of the generation, the process on ICFBC then pressurized by entering the unit ICFBC into pressurized container (pressurized vessel), hereinafter referred to as pressurized ICFBC (PICFBC). With this mechanism in addition to water vapor, will be produced also a high-pressure combustion gases that can be used to rotate so that the generation of gas turbines in combination (combined cycle) can be realized.Generation Coal Gasification Combined WithIncreasing the efficiency of generation with a combination of mechanisms through the use of synthetic gas gasification process results as in A-PFBC, the next generation of technology lead to further intensify the use of coal gasification technology into the generation system. This effort eventually resulted in the generation system called the Integrated Coal Gasification Combined Cycle (IGCC).Since this paper only discusses the development of power generation technology, then an explanation of how the coal gasification process takes place will not be described here.IGCCAn outline flow chart IGCC power generation system is shown in figure 12Figure 12. Typical IGCC(Source: Clean Coal Technologies in Japan, 2005) below.As shown in the figure, there are tools on the gasification system (gasifier) ​​used to produce gas, generally entrained flow type. Available on the market today for those types such as Chevron Texaco (now owned by GE Energy's license), E-Gas (formerly owned by Dow's license, then Destec, and last Conoco Phillips), and Shell. The working principle is the same all three devices, namely coal and high levels of oxygen incorporated into it and then performed the reaction of partial oxidation (partial oxidation) to produce synthetic gas (syngas), which is composed of over 85% of H2 and CO. Because the reaction takes place at high temperatures, ash in coal will melt and form a slag in a molten state (glassy slag). The heat generated by the gasification process can be used to generate high pressure steam, which then flowed into the steam turbine.Oxygen is used for the gasification process generated from the facility Air Separation Unit (ASU). This unit serves to separate the oxygen from the air through cryogenic separation mechanism, producing a yield of about 95% oxygen. In addition to oxygen, the ASU also produced nitrogen used as inert media for feeding coal into the gasifier, but can also be used to lower the temperature of the combustor so that NOx emissions can be controlled.In the synthesis gas, in addition to H2 and CO is also produced other elements that are not environmentally friendly such as HCN, H2S, NH3, COS, mercury vapor, and char.Therefore, the gas must be processed first to remove the part before it is sent to the gas turbine. Flue gas from the gas turbine and then flows to the Heat Recovery Steam Generator (HRSG) which serves to change the heat of the gas into water vapor, which then flowed into the steam turbine. With this mechanism, the efficiency of the resulting net generation is also far exceeds the generation of the regular system (PCC) that currently dominate. In addition to the generation efficiency, another advantage IGCC is very low emission levels of pollutants generated, fuel flexibility that can be used, water usage is 30-40% lower than conventional power plant (PCC), a significant level of CO2 capture, slag can be utilized to construction materials, and others - others.An example is the Nuon IGCC located in Buggenum, the Netherlands, with a capacity of 250mW. The plant produces a net efficiency of 43% (Low Heating Value), with the performance of environmental quality standards are very good. NOx emissions are produced very low at less than 10 ppm, then the sulfur removal efficiency above 99%, the level of flyash emissions, chloride compounds and volatile heavy metals that can be practically zero, and the waste water can be recirculated back so that no waste water disposal into the environment.In addition to these advantages, there are also weaknesses in the IGCC system developed at this time, for example, the amount of generation capacity is determined based on the number of units and gas turbine model to be used. Examples for GE Frame 7FA gas turbines with a capacity of 275MW. If IGCC will be operated with a generating capacity of 275MW, is quite a unit that is installed. When the second unit to be used, means the generation capacity to 550MW, and if 3 units it will be 825MW. Then when the desired generation capacity is under 200MW, then the model used is no longer the GE Frame 7FA, but GE 7FA with a capacity of 197MW. Similarly, if the generation capacity requires a smaller, then the GE 6FA a capacity of 85MW can be used.With the combination of model and number of gas turbine units to be used this, but will limit the generation capacity in the IGCC, is actually also will narrow the operating range. For example when going to lower the load at peak operation, it should be done by reducing the load on the gas turbine. Decrease the burden of this gas turbine will automatically lower the efficiency of generation and the consequences are less well on emissions of pollutants generated. Another weakness that need to be observed from the IGCC system today is the generation cost per kW and operation & maintenance (O & M) are more expensive, as well as the availability factor (AF) is lower than the PCC.IGCC history began in 1970 when the company STEAG of West Germany the expandable capacity of 170MW IGCC. Much later, demonstration project called Cool Water IGCC plant was launched in the U.S. in 1984, which operates a 120MW IGCC capacity until 1989. As of this writing, there is actually not a purely commercial IGCC units. The main cause is a large construction investments, as well as IGCC technology that has not been proven. IGCC technology here means the circuit of the entire building process (building blocks) that form the IGCC system intact. This needs to be emphasized because of their technology - for example, each unit in IGCC gasifier, HRSG, gas turbines, steam turbines, and the other is a proven technology. During the development of which lasted about 20 years since the Cool Water project, IGCC units are in commercial operation today both in the U.S. and in Europe in the first demonstration plant status. Examples of some of the IGCC plant is1. Tampa Electric Polk Power Station IGCC 250mW, located in Florida, USA. IGCC is operating since September 1996 under the Tampa project, using a gasifier of Chevron Texaco (now GE Energy). The fuel used is coal and petroleum coke (petcoke). The problem faced is more low carbon conversion rate compared with the planned value.Fauling had also occurred in the gas cooler.2. 260MW IGCC Wabash River Power Station, located in Indiana, USA. Operation since September 1995 under the Wabash River project, this plant uses gasification technology from Global Energy (now part of Conoco Phillips). Since the end of the project from the U.S. Department of Energy (DOE) in 2001, the fuel used is 100% petcoke.3. 250mW Nuon IGCC Power Station, located in Buggenum, Netherlands. This stems from IGCC Demkolec project that began in January 1994. The technology used is from Shell, the fuel is coal mixed with biomass (sludge and waste wood) to further reduce CO2 emissions. The problem that ever happened was a gas leak, the onset of cooler and cooler fauling on gas when mixed sludge of about 4-5%....

Figure 13. Nuon IGCC, Buggenum(Source: Thomas Chhoa, Shell Gas & Power, 2005)4. Elcogas 300MW IGCC Power Station, located in Puertollano, Spain. IGCC plant is in operation since June 1996 under the project Puertollano, using gasification technology from Prenflow (currently part of Shell). Fuel is a mixture of petcoke and coal ash 40% yield with a ratio of 50:50. Under the program of the European Union, this plant is planned as a place for the project taking CO2 (CO2 recovery) and H2 production.Taking into account various factors, including the generation of high efficiency, environmentally friendly factor, and a proven gasification technology, an effort to further reduce the weaknesses of IGCC have been started.Apart from cost, effort has also been conducted to further improve the efficiency of generation, namely by adding a fuel cell (fuel cell) into the IGCC system. Thus, there will be three types of combinations of generation in this new system of gas turbines, steam turbines, and fuel cell. Generation method is called with Integrated Coal Gasification Fuel Cell Combined Cycle (IGFC), the diagram shown in figure 16 alirnya below.Figure 14. Typical IGFC(Source: Clean Coal Technologies in Japan, 2005)In fuel cells, electricity generation is done directly through an electrochemical reaction between hydrogen and oxygen so that the energy loss rate and efficiency pembangkitannya little high. Hydrogen can be derived from natural gas, bio gas, or gases of coal gasification. Based on the material used for the electrolyte, the fuel cell is divided into 4-Phosphoric Acid Fuel Cell (PAFC), Molten Carbonate Fuel Cell (MCFC), Solid-Oxide Fuel Cell (SOFC) and Proton-Exchange Membrane Fuel Cell (PEFC). Below is shown the characteristics of the four types of fuel cells.Table 1. Characteristics of Fuel Cells(Source: Clean Coal Technologies in Japan, 2005)From the table above shows that fuel cells are suitable for combination with the generation of gas turbines is the SOFC, because the reaction produces very high temperatures.Compared with the PCC, the generation with IGFC method is theoretically capable of reducing CO2 emissions by 30%. Another plus is the high efficiency of the generation that can be achieved is at least 55%. Besides these advantages, there are several things to consider before IGFC really - really can be applied commercially. The first is the urgency of IGCC technology maturation, because IGFC basically is the development of IGCC. Then, the need for fuel cell development but low-cost high-efficiency, to support the generation cost competitive in the future.CoverDevelopments in power plant coal combustion technology has been presented above. In general it can be said that a growing technology does not depart from the principal so-called 3E, namely Engineering (technical side), Economy (the economy), and the Environment (the environment). In the early stages, Economy factor may be the primary consideration for the construction of generation facilities, followed by Engineering, and the last Environment. But along with efforts to reduce pollution or environmental contamination that caused the tightness of environmental quality standards, it appears that the order of 3E is starting to change. Environment factors are slowly ranks first in the consideration of technology development, and engineering, and last precisely Economy.Taking the example of IGCC, it is natural that the early stage of development would require a large fee. But along with the strengthening of environmental issues and the technology matures, it will decrease the cost and at a certain time would be competitive against existing technologies. Instead, the existing generation technologies, for example, which currently dominates the PCC, gradually will be more expensive to accommodate the environmental quality standards are increasingly stringent, and in the end it actually would cost in terms of economics. Showing below the generation cost comparison between IGCC and PCC in the U.S. over the last 20 years, and predictions in the future.Figure 15. Generation Cost Comparison IGCC and PCC per kW in the U.S.(Source: JCOAL Journal, vol.3, January 2006)From the chart above shows that over the last 20 years, the cost of generation for the PCC increased by about 50%. This increase is caused by the addition of equipment to reduce the environmental burden, such as facilities desulfurization (FGD). In contrast, the generation cost per kW at IGCC actually decline, and expected in 2010, its value will be equal to the PCC, which is about $ 1200.Reference1. Amick, Phil, Flexibility Coal Gasification for Fuels & Products, ConocoPhillips, 20052. Baardson, John A., Coal to liquids: Shell Coal Gasification with Fischer-Tropsch Synthesis, Baardson Energy LLC, 2003.3. Chhoa, Thomas, Shell Gasification Business in Action, Shell Gas & Power, 2005.4. JCOAL, Coal Science Handbook, the Japan Coal Energy Center, 2005.5. JCOAL, JCOAL Journal Vol. 2, nov. 2005, the Japan Coal Energy Center, 2005.6. JCOAL, JCOAL Journal Vol. 3, January 2006, the Japan Coal Energy Center, 2006.7. JCOAL, JCOAL Journal Vol. 4, mar. 2006, the Japan Coal Energy Center, 2006.8. Presentation Materials, Idemitsu Kosan Co.., Ltd., 2003.9. Sekitan no Kiso Chishiki, Sekitan Shigen Kaihatsu Kabushiki Kaisha.10. Shigen Enerugi Shigen Nenryou Bu-Chou, Ko-to-ru No. 2001 Nen Ban, Shigen Sangyou Shinbunsha, 2001.11. Sema, Tohru, Karyoku Hatsuden Souron, Denki Gakkai, 2002.12. WCI, The Coal Resource, World Coal Institute, 2004.

see also previous article "Chemical recovery boiler"

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CHEMICAL RECOVERY BOILER

HEART OF A CHEMICAL PULP MILL

The recovery boiler plays a central role in the chemical cycle of a modern pulp mill. The boiler produces energy for the mill.

The spent liquor from the digesting plant goes first to the evaporation plant where the dry solids content of the liquor is increased. Then the evaporated liquor comes to the recovery boiler plant. Fly ash from electrostatic precipitators is mixed into the black liquor.  After additional concentration of the black liquor in the evaporation plant  the liquor is burned in the combustion chamber of the boiler.

Feed water is pumped first to the economizers where it is preheated by flue gas. The water then enters the water circulation system of the boiler. During combustion of  the black liquor high pressure steam is generated in the boiler.  The superheated steam flows from boiler to a turbine generator plant.

The hot smelt flow of the regenerated chemicals is drained from the furnace floor to the dissolving tank. The chemicals are dissolved into weak white liquor and returned to a recausticizing plant for further processing.

EXPERIENCE

Manufacturing of steam boilers started in Varkaus, Finland, in 1872. The first boilers were used in vessels.  The first recovery boiler was manufactured in 1952 for Lohja-Kotka Oy, Finland.  The steam pressure was 45 bar and steam temperature 400 C. The dry solids combustion capacity of the boiler was 110 tons per day.  The combustion capacity of modern recovery boilers is about 30 times higher.see also previous article "Furnace camera"

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NCG (NON CONDENSIBLE GASES)

NCG Burning in Recovery Boilers This time i will explain about Non Condensible Gases or NCG in Power plant boiler.after yesterday I was talking about "How does a power plant boiler work?" NCG = Non Condensible Gases NCG are: the non-condensable gas, this gas has a very distinctive odor karesteristik. This odor is caused by a mixture of sulfur into TRS (Total Reduced Sulfur) Categories A.Composition and NCG NCG content include: Hydrogen sulfide (H2S) Mercaptan (CH3SH) Dimethyl sulfide (CH3) 2S Dimethyl disulfide (CH3) 2S2 Ethanol (C2H5OH) NCG gases are divided into two categories, namely: LVHC = Low Volume High Cocentration High Volume Low HVLC = Cocentration B. Sources of NCG NCG is the fuel in the RECOVERY BOILER sourced from: A. LVHC: a. Strippe gas b. Gas from the evaporator plan (VE) c. Faul VE Condensate Tank d. Digester plan (PULP MAKING) 2. HVLC: a. WBL Gas Tanks & Tank HBL 3 & VE b. Gas & PULP MAKING Design Data LVHC RB-1 Design Data Stripper Gas: Flow = 1550 Nm ³ / h Temp = 80 ° C Moisture = 48% Volume Gases from Evaporator Flow = 680 Nm ³ / h Temp = 50 ° C Moisture = 13% Volume Digester gas form Flow = 335 Nm ³ / h Temp = 90 ° C Moisture = 71%.see also previous article "Vacuum evaporator(VE)

Volume RB NCG SYSTEM (LVHC)

RB  ODOROUS GAS ( HVLC)

Odorous Gas

1.NCG CONTENT

2.CONCENTRATION 

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WHAT IS THE BLACK LIQUOR

Concentrated black liquor contains organic dissolved wood residue in addition to sodium sulfate from the cooking chemicals added at the digester. Combustion of the organic portion of chemicals produces heat. In the recovery boiler heat is used to produce high pressure steam, which is used to generate electricity in a turbine. The turbine exhaust, low pressure steam is used for process heating.

Combustion of black liquor in the recovery boiler furnace needs to be controlled carefully. High concentration of sulfur requires optimum process conditions to avoid production of sulfur dioxide and reduced sulfur gas emissions. In addition to environmentally clean combustion, reduction of inorganic sulfur must be achieved in the char bed.

The recovery boiler process has several unit processes:

• Combustion of organic material in black liquor to generate steam
• Reduction of inorganic sulfur compounds to sodium sulfide, which exits at the bottom as smelt
• Production of molten inorganic flow of mainly sodium carbonate and sodium sulfide, which is later recycled to the digester after being re-dissolved
• Recovery of inorganic dust from flue gas to save chemicals
• Production of sodium fume to capture combustion residue of released sulfur compounds

First recovery boilers

Some features of the original recovery boiler have remained unchanged to this day. It was the first recovery equipment type where all processes occurred in a single vessel. The drying, combustion and subsequent reactions of black liquor all occur inside a cooled furnace. This is the main idea in Tomlinson’s work.

Secondly the combustion is aided by spraying the black liquor into small droplets. Controlling process by directing spray proved easy. Spraying was used in early rotary furnaces and with some success adapted to stationary furnace by H. K. Moore. Thirdly one can control the char bed by having primary air level at char bed surface and more levels above. Multiple level air system was introduced by C. L. Wagner.

Recovery boilers also improved the smelt removal. It is removed directly from the furnace through smelt spouts into a dissolving tank. Some of the first recovery units employed the use of Cottrell’s electrostatic precipitator for dust recovery.

Babcock & Wilcox was founded in 1867 and gained early fame with its water tube boilers. The company built and put into service the first black liquor recovery boiler in the world in 1929.^[2] This was soon followed by a unit with completely water cooled furnace at Windsor Mills in 1934. After reverberatory and rotating furnaces the recovery boiler was on its way.

The second early pioneer, Combustion Engineering based its recovery boiler design on the pioneering work of William M. Cary, who in 1926 designed three furnaces to operate with direct liquor spraying and on work by Adolph W. Waern and his recovery units.

Recovery boilers were soon licensed and produced in Scandinavia and Japan. These boilers were built by local manufacturers from drawings and with instructions of licensors. One of the early Scandinavian Tomlinson units employed a 8.0 m high furnace that had 2.8*4.1 m furnace bottom which expanded to 4.0*4.1 m at superheater entrance.^[3]

This unit stopped production for every weekend. In the beginning economizers had to be water washed twice every day, but after installation of shot sootblowing in the late 1940s the economizers could be cleaned at the regular weekend stop.

The construction utilized was very successful. One of the early Scandinavian boilers 160 t/day at Korsnäs, operated still almost 50 years later.^[4]

Development of recovery boiler technology

The use of Kraft recovery boilers spread fast as functioning chemical recovery gave Kraft pulping an economic edge over sulfite pulping.^[4]

The first recovery boilers had horizontal evaporator surfaces, followed by superheaters and more evaporation surfaces. These boilers resembled the state-of-the-art boilers of some 30 years earlier. This trend has continued until today. Since a halt in the production line will cost a lot of money the adopted technology in recovery boilers tends to be conservative.

The first recovery boilers had severe problems with fouling.^[5]

Tube spacing wide enough for normal operation of a coal fired boiler had to be wider for recovery boilers. This gave satisfactory performance of about a week before a water wash. Mechanical sootblowers were also quickly adopted. To control chemical losses and lower the cost of purchased chemicals electrostatic precipitators were added. Lowering dust losses in flue gaseshas more than 60 years of practice.

One should also note square headers in the 1940 recovery boiler. The air levels in recovery boilers soon standardized to two: a primary air level at the char bed level and a secondary above the liquor guns.

In the first tens of years the furnace lining was of refractory brick. The flow of smelt on the walls causes extensive replacement and soon designs that eliminated the use of bricks were developed.

Improving air systems

To achieve solid operation and low emissions the recovery boiler air system needs to be properly designed. Air system development continues and has been continuing as long as recovery boilers have existed.^[6] As soon as the target set for the air system has been met new targets are given. Currently the new air systems have achieved low NOx, but are still working on lowering fouling. Table 1 visualizes the development of air systems.

Table 1: Development of air systems.^[6]

Air system	Main target	But also should
1st generation	Stable burning of black liquor
2nd generation	high reduction	Burn liquor
3rd generation	decrease sulfur emissions	Burn black liquor, high reduction
4th generation	low NOx	Burn black liquor, high reduction and low sulfur emission
5th generation	decrease superheater and boiler bank fouling	Burn black liquor, high reduction, low emissions

The first generation air system in the 1940s and 1950s consisted of a two level arrangement; primary air for maintaining the reduction zone and secondary air below the liquor guns for final oxidation.^[7]The recovery boiler size was 100 – 300 TDS (tons of dry solids) per day. and black liquor concentration 45 – 55 %. Frequently to sustain combustion auxiliary fuel needed to be fired. Primary air was 60 – 70 % of total air with secondary the rest. In all levels openings were small and design velocities were 40 – 45 m/s. Both air levels were operated at 150^oC. Liquor gun or guns were oscillating. Main problems were high carryover, plugging and low reduction. But the function, combustion of black liquor, could be filled.

The second generation air system targeted high reduction. In 1954 CE moved their secondary air from about 1 m below the liquor guns to about 2 m above them.^[7] The air ratios and temperatures remained the same, but to increase mixing 50 m/s secondary air velocities were used. CE changed their frontwall/backwall secondary to tangential firing at that time. In tangential air system the air nozzles are in the furnace corners. The preferred method is to create a swirl of almost the total furnace width. In large units the swirl caused left and right imbalances. This kind of air system with increased dry solids managed to increase lower furnace temperatures and achieve reasonable reduction. B&W had already adopted the three-level air feeding by then.

Third generation air system was the three level air. In Europe the use of three levels of air feeding with primary and secondary below the liquor guns started about 1980. At the same time stationary firing gained ground. Use of about 50 % secondary seemed to give hot and stable lower furnace.^[8] Higher black liquor solids 65 – 70 % started to be in use. Hotter lower furnace and improved reduction were reported. With three level air and higher dry solids the sulfur emissions could be kept in place.

Fourth generation air systems are the multilevel air and the vertical air. As the feed of black liquor dry solids to the recovery boiler have increased, achieving low sulfur emissions is not anymore the target of the air system. Instead low NOx and low carryover are the new targets.

[edit]Multilevel air

The three-level air system was a significant improvement, but better results were required. Use of CFD models offered a new insight of air system workings. The first to develop a new air system was Kvaerner (Tampella) with their 1990 multilevel secondary air in Kemi, Finland, which was later adapted to a string of large recovery boilers.^[9] Kvaerner also patented the four level air system, where additional air level is added above the tertiary air level. This enables significant NOx reduction.

[edit]Vertical air

Vertical air mixing was invented by Erik Uppstu.^[10] His idea is to turn traditional vertical mixing to horizontal mixing. Closely spaced jets will form a flat plane. In traditional boilers this plane has been formed by secondary air. By placing the planes to 2/3 or 3/4 arrangement improved mixing results. Vertical air has a potential to reduce NOx as staging air helps in decreasing emissions.^[11] In vertical air mixing, primary air supply is arranged conventionally. Rest of the air ports are placed on interlacing 2/3 or 3/4 arrangement.

Black liquor dry solids

Net heating values of industrial black liquors at various concentrations

As fired black liquor is a mixture of organics, inorganics and water. Typically the amount of water is expressed as mass ratio of dried black liquor to unit of black liquor before drying. This ratio is called the black liquor dry solids.

If the black liquor dry solids is below 20 % or water content in black liquor is above 80 % the net heating value of black liquor is negative. This means that all heat from combustion of organics in black liquor is spent evaporating the water it contains. The higher the dry solids, the less water the black liquor contains and the hotter the adiabatic combustion temperature.

Black liquor dry solids have always been limited by the ability of available evaporation.^[12] Virgin black liquor dry solids of recovery boilers is shown as a function of purchase year of that boiler.

Virgin black liquor dry solids as a function of purchase year of the recovery boiler

When looking at the virgin black liquor dry solids we note that on average dry solids has increased. This is especially true for latest very large recovery boilers. Design dry solids for green field mills have been either 80 or 85 % dry solids. 80 % (or before that 75 %) dry solids has been in use in Asia and South America. 85 % (or before that 80 %) has been in use in Scandinavia and Europe.

[edit]High temperature and pressure recovery boiler

Development of recovery boiler main steam pressure and temperature was rapid at the beginning. By 1955, not even 20 years from birth of recovery boiler highest steam pressures were 10.0 MPa and 480^oC. The pressures and temperatures used then backed downward somewhat due to safety.^[13] By 1980 there were about 700 recovery boilers in the world.^[8]

Development of recovery boiler pressure, temperature and capacity.

[edit]Safety

One of the main hazards in operation of recovery boilers is the smelt-water explosion. This can happen if even a small amount of water is mixed with the solids in high temperature. Smelt-water explosion is purely a physical phenomenon. The smelt water explosion phenomena have been studied by Grace.^[14] By 1980 there were about 700 recovery boilers in the world.^[8] The liquid - liquid type explosion mechanism has been established as one of the main causes of recovery boiler explosions.

In the smelt water explosion even a few liters of water, when mixed with molten smelt can violently turn to steam in few tenths of a second. Char bed and water can coexist as steam blanketing reduces heat transfer. Some trigger event destroys the balance and water is evaporated quickly through direct contact with smelt. This sudden evaporation causes increase of volume and a pressure wave of some 10 000 – 100 000 Pa. The force is usually sufficient to cause all furnace walls to bend out of shape. Safety of equipment and personnel requires an immediate shutdown of the recovery boiler if there is a possibility that water has entered the furnace. All recovery boilers have to be equipped with special automatic shutdown sequence.

The other type of explosions is the combustible gases explosion. For this to happen the fuel and the air have to be mixed before the ignition. Typical conditions are either a blackout (loss of flame) without purge of furnace or continuous operation in a substoichiometric state. To detect blackout flame monitoring devices are installed, with subsequent interlocked purge and startup. Combustible gas explosions are connected with oil/gas firing in the boiler. As also continuous O₂ monitoring is practiced in virtually every boiler the noncombustible gas explosions have become very rare.

[edit]Modern recovery boiler

The modern recovery boiler is of a single drum design, with vertical steam generating bank and wide spaced superheaters. This design was first proposed by Colin MacCallum in 1973 in a proposal by Götaverken (now Metso Power inc.) for a large recovery boiler having a capacity of 4,000,000 lb of black liquor solids per day for a boiler in Skutskär, Sweden, but this design was rejected as being too advanced at that time by the prospective owner. MacCallum presented the design at BLRBAC and in a paper "The Radiant Recovery Boiler" printed in Tappi magazine in December 1980. The first boiler of this single-drum design was sold by Götaverken at Leaf River in Mississippi in 1984. The construction of the vertical steam generating bank is similar to the vertical economizer. Vertical boiler bank is easy to keep clean. The spacing between superheater panels increased and leveled off at over 300 but under 400 mm. Wide spacing in superheaters helps to minimize fouling. This arrangement, in combination with sweetwater attemperators, ensures maximum protection against corrosion. There have been numerous improvements in recovery boiler materials to limit corrosion.^{[15][16][17][18]}

The effect of increasing dry solids concentration has had a significant effect on the main operating variables. The steam flow increases with increasing black liquor dry solids content. Increasing closure of the pulp mill means that less heat per unit of black liquor dry solids will be available in the furnace. The flue gas heat loss will decrease as the flue gas flow diminishes. Increasing black liquor dry solids is especially helpful since the recovery boiler capacity is often limited by the flue gas flow.

A modern recovery boiler consists of heat transfer surfaces made of steel tube; furnace-1, superheaters-2, boiler generating bank-3 and economizers-4. The steam drum-5 design is of single-drum type. The air and black liquor are introduced through primary and secondary air ports-6, liquor guns-7 and tertiary air ports-8. The combustion residue, smelt exits through smelt spouts-9 to the dissolving tank-10.

The nominal furnace loading has increased during the last ten years and will continue to increase.^[19] Changes in air design have increased furnace temperatures.^{[20][21][22][23]} This has enabled a significant increase in hearth solids loading (HSL) with only a modest design increase in hearth heat release rate (HHRR). The average flue gas flow decreases as less water vapor is present. So the vertical flue gas velocities can be reduced even with increasing temperatures in lower furnace.

The most marked change has been the adoption of single drum construction. This change has been partly affected by the more reliable water quality control. The advantages of a single drum boiler compared to a bi drum are the improved safety and availability. Single drum boilers can be built to higher pressures and bigger capacities. Savings can be achieved with decreased erection time. There is less tube joints in the single drum construction so drums with improved startup curves can be built.

The construction of the vertical steam generating bank is similar to the vertical economizer, which based on experience is very easy to keep clean.^[24] Vertical flue gas flow path improves the cleanability with high dust loading.^[25] To minimize the risk for plugging and maximize the efficiency of cleaning both the generating bank and the economizers are arranged on generous side spacing. Plugging of a two drum boiler bank is often caused by the tight spacing between the tubes.

The spacing between superheater panels has increased. All superheaters are now wide spaced to minimize fouling. This arrangement, in combination with sweetwater attemperators, ensures maximum protection against corrosion. With wide spacing plugging of the superheaters becomes less likely, the deposit cleaning is easier and the sootblowing steam consumption is lower. Increased number of superheaters facilitates the control of superheater outlet steam temperature especially during start ups.

The lower loops of hottest superheaters can be made of austenitic material, with better corrosion resistance. The steam velocity in the hottest superheater tubes is high, decreasing the tube surface temperature. Low tube surface temperatures are essential to prevent superheater corrosion. A high steam side pressure loss over the hot superheaters ensures uniform steam flow in tube elements.

[edit]Future prospects

Recovery boilers have been the preferred mode of Kraft mill chemical recovery since the 1930s and the process has been improved considerably since the first generation. There have been attempts to replace the Tomlinson recovery boiler with recovery systems yielding higher efficiency. The most promising candidate appears to be gasification,^[26][27] where Chemrec's technology for entrained flow gasification of black liquor could prove to be a strong contender.^[28]

Even if new technology is able to compete with traditional recovery boiler technology the transition will most likely be gradual. First, manufacturers of recovery boilers such as Metso, Andritz andMitsubishi, can be expected to continue development of their products. Second, Tomlinson recovery boilers have a long life span, often around 40 years, and will probably not be replaced until the end of their economic lifetime, and may in the meantime be upgraded at intervals of 10 – 15 years.

see also previous article "Ncg (non condensible gases)"

May be useful.

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MECHANISMS OF STEAM SOOT BLOWER EROSION

There are many mechanisms that can cause steam soot blower erosion of boiler tubes at various heat transfer sections. Knowing the way these mechanisms contribute to erosion will help to prevent loss of availability of boiler.

Soot blowers are provided in boilers at various locations like water-walls, superheaters, reheaters, economizers and air pre-heaters. Steam soot blowers have specific advantage and disadvantages over other types. The advantages being mainly their low capital cost, operating cost and the effectiveness of cleaning in areas like furnace, superheaters and reheaters.

The major disadvantages are they need a higher level of maintenance; effectiveness is low in oil firing mainly in air pre-heater area. They need warm up and condensate draining before startup. The mechanisms of steam soot blower erosion of heat transfer tubes can be a single factor or multiple factors acting individually or in unison. There are much more than hundred soot boilers in boilers generating and supplying steam for a 500 MW and above plants.

Possible mechanisms

• All blowers are set to be set at the right steam pressure recommended by the designer if this is not done then it leads to poor cleaning or higher rate of tube erosion due to high steam pressure. This is true for all soot blowers in the boiler starting from furnace to air pre-heater.
• The alignment of the blower with respect to the furnace walls, superheater tubes, reheater tubes, economizer tubes and air pre-heater tubes or elements is very critical and not maintaining this leads to erosion of the tubes and subsequent metal wastage. The thinning of the tubes finally leads to pinhole failures and many secondary figures due to this depending upon the orientation of the leak.
• It is required to ensure at least 50 degree centigrade of super heat in the steam being used for blowing. If the super heat in the steam is lower than required then during blowing wet steam impinge the tubes at high velocity and the impact force damaging the heat transfer tubes. This can be identified by the typical spit like metal wastage on the tubes surrounding the blower’s area of effectiveness.
• The duration of operation of blowers is another main reason for erosion of the heat transfer tubes. Even if you maintain the correct pressure and temperature the erosion will take place at a slow phase if duration is more than required.
• In coal fired boiler if alignment is not correct then the ash deposits being cleaned can get entrained and cause erosion of tubes. However in oil fired boilers it is not a mechanism that can happen due to the fact that the ash in oil is not significant at all.
• The higher frequency of operation of the soot blowers than needed also leads to tube erosion.
• Optimizing the soot blower operation is important as operating those blowers where deposits are not there or very low will lead to metal wastage over a period of time.
• Failure to drain the condensate in the soot blower steam pipes is also contributing mechanism of tube erosion. The condensate gets entrained in the steam while the blower operates and has a much higher damaging effect than the lower degree of superheat in steam.

It has been seen in many boilers, mainly coal fired boilers, the soot blower erosion is one of the main contributing factors for loss of boiler availability. In the case of chemical recovery boilers also the soot blowers attribute to the loss of availability of boiler in a significant way

Soot blowers keep the heat transfer surfaces in a boiler clean. A brief description of the working of soot blowers is given in this article.

Chimney Sweeps have been legendary characters in English literature from Hans Christian Anderson to Charles Dickens. In the earlier days when houses had fireplaces, the Chimney Sweep did the function of cleaning the soot from the chimney. In the modern day boiler, the soot blower does the same function.

In oil fired boilers, over a period of time the heat transfer tubes get covered by a layer of soot or fine carbon deposit. This reduces the heat transfer from the hot gases to the water and reduces the efficiency of the boiler.

In coal fired boilers, the furnace area gets covered by slag which is molten ash. The ash also sticks to the heat transfer surface in the other heat transfer areas. These ash accumulations reduce heat transfer and increase the tube metal temperatures leading to failure of the tubes.

.

Tube cleaning is done periodically to remove the ash or soot deposits. Steam is the medium used for cleaning. The steam is taken from the boiler itself.

The soot blower consists of a lance tube with a nozzle at the end. When it is operated, the lance is extended into the boiler and steam is admitted through the lance. The steam comes out as a high velocity jet through the nozzles, which cleans the ash deposited on the surface. When the lance moves into the boiler it is also rotating so that it cleans the sweeping area covered by the circular travel of the nozzle. The lance is then retracted back.

There are two types of soot blowers.

• One with a very long lance called the “long retractable soot blowers.” This is normally used to clean the ash deposit from between the coils of superheaters and economisers.

• The other type is the shorter lance type called the “wall blowers.” These are used to clean the furnace walls. The lance extends a short distance around 200 mm from the furnace wall. The nozzle direction is such that the steam impinges on the walls cleaning the surface. During operation, the lance rotates cleaning the radial area covered by the steam from the nozzle.

The deposits on the walls are due to the chemical constituents of ash, and the amount of combustion air. If the ash contains more of Ferrous Sulphide, then the melting temperature of the ash is low which makes the ash melt and stick to the walls.

A large coal fired Thermal power plant will have around two hundred soot blowers of both types arranged to cover all the area of the boiler. This will be programmed to automatically operate to a required sequence.

Intelligent soot blower systems calculate the trends in the temperature increase in different sections of a boiler. The program then decides which soot blowers have to be operated and at what frequency.

High-pressure water lances are also used in some units where the slagging is very heavy.

see also previous article "What is the black liquor?"

May be useful.

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FURNACE CAMERA

This day i will taking about Furnace Camera.As the current technological developments in power plant technology especially the use of recovery boiler is constantly innovating in order to complement the existing deficiencies in the means of production to facilitate the operation of the recovery boiler.

Currently the power plant that uses a recovery boiler there is a lack of technology to the unavailability of a device to control the conditions inside the boiler (furnace). So far the recovery boiler operator can only monitor the condition of the inside of the furnace manually just by looking at the field by controlling the air of room pannel (dcs). but that's not enough data taken with the actual data. accuracy conditions may only be 65% to monitor conditions inside the furnace charbed.

               

Camera Enclosure with Lens

The above shows what is removed and store during shutdown or repair

Camera Enclosure Interior

Back of camera core

Removing Camera Core

Camera Retract system

Camera Port

Cleaner

Control Enclosure

Solenoid valve assembly

(Inside control enclosure)

Valve Manual override

Siemens LOGO PLC

Settable Parameter available from key pad on Logo:

Cycle time (time between cleaning cycles)

Cleaning stroke time (time energized and de-energized

Number of cleaning strokes

 

Pneumatic System

Lens tube/manifold pressure to be maintained between 1.5 and 2 BAR

Input pressure to the system should be 5 and 12 bar

The cleaning cylinder (with check valve) acts as an accumulator to retract camera in the event of a line failure.

System Faults and General Maintenance

LENS CLEANING

The most common form of maintenance on the camera lens system will be cleaning the “objective” lens – that part of the lens system furthest from the camera. Periodic, daily cleaning of the objective lens should be expected, although cleaning intervals of 5 or 6 days are not un-common.

A dirty objective will produce an image that is fuzzy or appears out of focus. The part of the objective that requires cleaning is the protective clear sapphire window, which is very hard and difficult to inadvertently scratch, but relatively easy to break.

Warning:

Do not attempt to clean a hot lens! The objective lens assembly must be below 110°F or comfortable to the touch before cleaning.

To clean the objective lens sapphire:

Retract the lens by selecting “RETRACT” at the control enclosure.

Allow the lens to cool for several minutes.

Once cool (relatively comfortable to the touch), turn the supply air to the lens system off at the shut-off valve.

Using a cotton swab and alcohol, reach into the end of the lens assembly and clean any dirt or oil that may have collected on the objective sapphire.

Char build-up on or around the lens tube should also be cleaned at this time.

Turn the supply air on.

Most Faults and the probable reason for the fault are broadcast on the face of the Control Panel

The camera has 30-seconds to cool down once an overtemp

Situation is discovered.

There are three different faults that will cause the camera to retract:

Camera enclosure over temp - temporary over temp recognized

Camera has retracted and then cooled to operating temp check air supply and for combustion air leaks

Camera over temp - system is shut down

Camera retracted and failed to cool within 30 seconds camera has been shut off as result to avoid damage. Check air supply and cooler adjustment.

Low air pressure – camera retracted to avoid overheating

Check for compressed air leaks and ball valve position

Retract limit fail – automatic cleaning not possible

Important to keep the retract cleaned and lubricated so if a overtemp condition occurs the retract can do what it is supposed to do

Output fail check fuse 1

Output fail check fuse 2

Output fail check fuse 3

There are three different ouput faults that are monitored

Maybe usefull.

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