International Journal of Emerging Trends in Science and Technology Optimization of soot blower control

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1 International Journal of Emerging Trends in Science and Technology Optimization of soot blower control Bharathi.P Nandhini.R Dheepika.S Valli.M Abstract- Boiler is one of the main equipment in thermal power plant. The Soot, ash on the surface of boiler tubes is still a great concern and affecting the efficiency of the coal fired boiler. At present soot blowers are operated manually in every shift. This project presents one of the embedded based industrial automation techniques for efficient operation of the soot blowers in both auto and manual mode, which also adopts the stack based temperature controlling of soot blower for optimization of soot blower control to increase the boiler efficiency. An automation technique is simulated in real time using PROTEUS and designed in ATMEGA328 (ARDUINO UNO BOARD) 1. INTRODUCTION An Efficient boiler burns the coal to produce heat energy which is transferred to the water for steam production. Due to boiler losses such as heat transfer fouling, poor combustion, poor maintenance and operation 100% efficiency of the boiler cannot be reached.hence the boiler operation and its accessory controls has to be monitored carefully. Input-Output method and heat loss method are the two ways of evaluating the boiler efficiency. In heat loss method, the boiler efficiency is evaluated by subtracting overall boiler losses from maximum theoretical boiler efficiency. The following are the boiler losses associated with indirect method. 1. Loss due to the heat carried by the dry flue gas through the chimney. 2. Loss in the form of heat carried away by the moisture 3. Loss in the form of heat radiation from the outer surfaces of the boiler. 4. Loss due to incomplete combustion. Among all these losses, the maximum is loss due to dry flue gas. The main reason for increase in stack temperature is due to the deposition of soot on heat transfer surfaces. Due to incomplete combustion and low grade coal soot is deposited on the surface of the tubes and due to improper treatment of water there may be concentration of salts that are responsible for the formation of scale on the surface of the water tubes. Due to this there is a possibility of reduction in boiler efficiency. Generally coal is used as the fuel in all thermal based power plants and water tube boilers are preferred for giving water as input to the boiler. Due to the use of low grade coal soot formation takes place which reduces the heat transfer rate to the water tubes and reduces the efficiency. Hence soot blowers are used in power plants for removing the deposition of soot over the surfaces. Steam is injected through a nozzle with high pressure. When this high pressure steam is impacted over the tube surfaces the soot can be removed gradually. 2. DRAWBACK OF CONVENTIONAL SYSTEM In the conventional system the soot blowers are controlled using PLC technology. The number of Bharathi.P Page 696

2 soot blowers in a power plant is around 80. Using PLC technology for control purpose requires separate control system for each soot blowers. In the conventional system the soot blowers are operated in two modes namely manual and automatic modes of operation. Inboth the modes the soot blowers perform three functions: forward Motion, rotating motion and retracting motion. The period of operation is fixed for all soot blowers irrespective of their position along the walls of the boiler. The soot deposition on the soot blowers placed near the top of the boiler is comparatively less to the soot deposition on the blowers that are placed at the bottom that is near to the coal burning area. The Operation of all the soot blowers irrespective of their position on the walls of the boilers results in wastage of steam. The steam requirement for the soot blowers on the top of the boiler will be less compared to the steam requirement for the blowers on the bottom of the boiler.in industry three phase induction motors are used as soot blower motors. The boiling temperature inside the boiler is very high and if the soot blowers are introduced deep into the boiler the high temperature may damage the soot blower. Hence a limiting switch is used to limit the motion of soot blowers. The limiting switch is used in all the functions of the soot blower. There is a possibility of some mechanical damage to the limiting switches which may interrupt the working of the soot blowers. 3. APPROXIMATE EFFICIENCY CALCULATION Let Total Energy Input = Total Energy Output = 100% Then let's assume that the proportion of the energy input going to the gas turbine (A) and to the waste heat recovery steam generator (B) is around: A = 1/3 = 33.33% B = 1-1/3 = 2/3 = 66.67% The energy input to the steam generator is then split into 85% (up to 90%) being recovered as steam energy in the boiler while the balance of 15% (or 10%) is lost to the atmosphere (smoke Because of this the requirement of cable is more. This also increases the difficulty of the wiring system. stack, radiation and convection loss). The steam energy is then captured in the steam turbine with an efficiency of 37% and the balance (63%) is lost to the cooling water in the condenser. The mechanical energy captured in the turbine shaft is then coupled in a clutch (100% efficiency) to drive finally the electric generator (EG) with mechanical to electrical conversion efficiency of 98% (balance of 2% lost to heating in the generator windings and generator cooling system). The final formula is thus: OE = (A x TE + B x BE x STE) x ME x GE Where OE = overall energy efficiency, % of fuel energy input (as GHV or LHV) A= 1/3 = 33.33% (assumption) TE = turbine efficiency = say 85% - 95% B= 1 - A = 1-1/3 = 2/3 = 66.67% (balance) BE = boiler efficiency = 50 %( upto60%) = function of exit flue gas temperature (energy lost), turbine exhaust temperature (energy input), boiler design, flue gas. STE = steam turbine efficiency = 37% (up to 40%) = function of steam inlet temperature, steam exhaust pressure, condenser vacuum pressure, cooling system, steam turbine design, steam quality, function of heat loss from turbine due to conduction, convection and radiation from turbine casing, any heat loss due to friction resulting in higher exhaust is captured, however, by the heat recovery steam generator ME = mechanical drive shaft and clutch efficiency = 100% = function of drive shaft design, clutch system, mechanical design, wind age losses (air drag) GE = electric generator efficiency = 98% = function of generator design, voltage, wind age losses (air drag). Putting all together now, the predicted and approximate overall thermal efficiency of the power plant is: OE = (33.33% x 85% % x 50% x 37%) x 100% x 98% = 39.85% Bharathi.P Page 697

3 4. GENERAL RULES RELATING TO AN INDUSTRIAL BOILER The fuel system includes various components like valves, gauges, burners to provide the necessary fuel, so as to generate heat. The components of fuel system mainly depend on the type of fuel used for combustion. The following are the some of the general rules related to an industrial boiler : 1 % boiler efficiency increases, if 5 % excess air is reduced. Boiler efficiency increases by 1 % if the flue gas temperature is reduced by 22 C. Boiler fuel consumption reduces by 1 % when the feed water temperature rises by 6 C. 1 % fuel would be saved when the combustion air temperature increases by 20 C. 2.5 % fuel consumption increases due to 3 mm thick soot deposition on a heat surface. Fuel consumption increases by 5 to 8 % when a 1mm thick scale deposits on the water side. 5. ADVANTAGES OF SOOT BLOWER CONTROL Excess air is reduced, the flue gas temperature is reduced, feed water temperature rises. Fuel consumption decreases saved when the combustion air temperature increases. Rapid increase in main steam temperature. According to the rules as mentioned above and advantages of soot blower control, the boiler efficiency is increased by 5% to 10%. So approximate and overall thermal efficiency of the power plant is: OE = (33.33% x 85% % x 55% x 37%) x 100% x 98% = 41.05% (Note: The overall efficiency of power plant increases nearly 2% to3% by having soot blower with temperature controlled mode.) 6. SOFTWARE DETAILS Simulation is the imitation of the operation of a real-world process or system over time. The act of simulating something first requires that a model be developed. Software used: Proteus 8 Proteus 8 is simulation software for various designs with microcontroller. It is mainly popular because of availability of almost all microcontrollers in it. So it is a handy tool to test programs and embedded designs. The features are as follows: Use of the Labcenter EasyHDL scripting language to define arbitrary signal chains via scriptable generators. Graph based simulation of all the aforementioned analyses types. CPU Models available for popular microcontrollers such as the PIC and 8051 series Graphs display analogue, digital and bus data. Frequency plots show gain and phase in db or linear measurements. Audio Analysis computes a waveform and plays it to your sound-card. Results can be exported as a *.wav file (and later imported via the audio generator if required). Interactive Analysis runs an interactive simulation and captures the results onto a graph Take accurate measurements using graph cursors. Export simulation results to other software (e.g. Excel) in CSV format. Interactive peripheral models include LED and LCD displays, a universal matrix keypad, an RS232 terminal and a whole library of switches, pots, lamps, LEDs etc. Virtual Instruments include voltmeters, ammeters, a dual beam oscilloscope and a 24 channel logic analyser. Digital simulator includes a BASIC-like programming language for modelling and test vector generation. A design created for simulation can also be used to generate a net list for creating a PCB - there is no need to enter the design a second time. 7. PLATFORM FOR SIMULATION DESIGN Bharathi.P Page 698

4 Intelligent Schematic Input System is an architecture that is used for developing the circuit that has to be implemented and testing its operation. The microcontroller used for our project is ATmega328. ISIS has the features to implement the function of the microcontroller that is used in this project. Moreover the function of the elements that is used in this project can be implemented. The features are as follows: Runs on windows 98/xp/Me/2k and later. Automatic wiring and dot replacement Powerful tool for selecting object and assigning properties. Total support for buses including connecting pins, intersheet terminal, modules and ports. It suits for all PCB layout. 8. BLOCK DIAGRAM FOR TIME AND TEMP MODE In the conventional system, there is only manual and automatic mode of operation of soot blowers but we are providing time and temperature control in addition to manual and automatic control with the help of ARDUINO UNO. K type thermocouple is a temperature sensing device which is consisting of Chromel and Alumel and it has the measurement range from 200 C to C. The output voltage range of K type thermocouple is very small for that we are using MAX31855 which is Cold-Junction Compensated Thermocouple-to-Digital Converter and gives corresponding digital signal to ARDUINO UNO. The software code is uploaded in the ARDUINO UNO; according to the digital signal from MAX31855 the control signal from ARDUINO UNO is given to the relay to actuate soot blower motors. 9. SIMULATION MODEL 10. WORKING First of all the main control to start the operation of the soot blowers is based on the main steam signal and home position. The soot blowers will operate only when the blowers are at their home position and all the input steam valve must be opened. In conventional system only manual and automatic mode of operation is used. Using arduino a third mod called as time and temp mode can be implemented for effective control of the steam input. When a mode is selected through the virtual monitor the corresponding motor of the soot blower is rotated by giving the control signal. Then the motor rotates in one direction for required delay, after that the control signal is given for the rotary function of the soot blower. The soot blower rotates for the delay period according to the soot formation then the control signal is sent for the retracting motion of the soot blower. Each mode is given in detail below. Manual Mode The control signals from main steam and home position switches are given to the arduino.type m in the serial monitor appearing in the laptop screen for mode selection. Now the control is given to the manual mode switches. The switches are operated through signal from the control room and the required soot blower can be selected for operation. Automatic Mode The soot blower prototypes are operated in sequence automatically as we type a in the virtual monitor Time & Temperature Mode (Time & Temp) For going into this mode we have to type t in the virtual monitor. First the initial temperature is Bharathi.P Page 699

5 displayed by getting the analog value from thek type thermocouple temperature sensor in the analog port appointed for it after a finite delay as given in program the final temperature is displayed on the screen. Based on the temperature difference the soot blower is rotated according to the delay calculations shown below, Let the initial temperature be T1 and final be T2 The temperature difference, ΔT = T1 T2... (1) The junction of each type thermocouple produces a specific millivoltage across it at a specific temperature. A thermocouple consists of two junctions connected in opposition. One is the measuring junction and the other is the reference junction. V D is the millivoltage resulting from the difference between the millivoltages generated by the two opposing junctions. V D is the millivoltage read when a meter is connected across the thermocouple. TO DETERMINE THE MEASURING JUNCTION TEMPERATURE Measure the "V D " millivoltage as shown above. Measure the actual temperature of the reference junction with a thermometer. Go to the table for the thermocouple being used and look up the millivoltage produced at that temperature. Add that millivoltage to the millivoltage measured as "V D " to get a total. Find that millivoltage total in the reference table. The corresponding temperature is the temperature of the measuring junction The reference table for K type thermocouple can be obtained at Now the delay is calculated based on the soot formation as t = 600/ (ΔT +10). 12. CONCLUSION In this project, design and implementation of real time optimization of soot blower control system is done. The soot blower control system is designed and implemented using Atmega328, ARDUINO UNO and is presented as a prototype model. This real time embedded based automated system whose operation depends upon stack temperature can be used for controlling the soot blower motor, instead of conventional method. This will definitely improve the boiler efficiency. Because of the use of Atmega328 microcontroller the system is more reliable, compact and economical. In this way, the system can be viewed as low cost design for process industry. 11. SIMULATION OUTPUT OF TIME AND TEMP MODE Bharathi.P Page 700