Presentation on theme: "September 23, 20041 Combustion Control for Boilers."— Presentation transcript:
September 23, Combustion Control for Boilers
September 23, Contents 1.Introduction 2.Basic type of boilers. 3.Why need boiler controls? 4.Combustion control for boilers. 5.Fujis oxygen gas analyzer.
September 23, Introduction How does a boiler works? A boiler is a water containing vessel which transfers heat from a fuel source (oil, gas or coal) into steam which is piped to a point where it can be used to run production equipment, to sterilize, to provide heat, to steam-clean, etc. The energy given up by the steam is sufficient to convert it back into the form of water. When 100% of the steam produced is returned to be reused, the system is called a closed system. Since some processes can contaminate the steam, so it is not always desirable to feed the condensate back into the boiler. A system that does not return the condensate is called an open system.
September 23, Introduction Closed system
September 23, Introduction Open system
September 23, Basic type of boilers. The two main types of boilers are: 1.Firetube 2.Watertube
September 23, Basic type of boilers. 1.Firetube Fire or hot gases are directed through the inside of tubes within the boiler shell which are surrounded by water. The tubes are arranged in banks so that the gases can be passed through the boiler up to 4 times before passing out the stack. This system exposes the maximum heat transfer surface to the water. Firetube boilers are also known as shell boilers and can produce up to approximately 750 hp or 25,000 lbs of steam per hour. 80% of boilers in use are of this configuration.
September 23, Basic type of boilers. 1.Firetube
September 23, Basic type of boilers. 1.Firetube
September 23, Basic type of boilers. 2.Watertube Fire or hot gases are directed to and around the outside of tubes containing water, arranged in a vertical position. Watertube boilers are usually rectangular in shape and have two or more drums. The separation of steam and water takes place in the top drum, while the bottom drum serves as a collection point for sludge. This system is usually used when more than 750 hp or several hundred thousand lbs of steam per hour, are needed. There are other designs with special configurations, adapting them to particular applications
September 23, Basic type of boilers. 2.Watertube
September 23, Basic type of boilers. 2.Watertube
September 23, Why need boiler controls? Boiler efficiency relates the boilers energy output to the boilers energy input and can be expressed as:- Boiler efficiency (%) = Heat exported by fluid/Heat provided by fuel An accurate control of the amount of air is essential to the boiler efficiency. Too much air will cool the furnace and carried away useful heat. And too little air and the combustion will be incomplete. Unburned fuel will be carried over and smoke may be produced.
September 23, Why need boiler controls? 1.Increase uptime and availability 2.Reduce flue gas emissions 3.Maintain boiler safety 4.Control operating costs
September 23, Why need boiler controls? 1.Increase uptime and availability The primary objective of most boilers operation is maintaining the uptime and availability. It is essential to maintain and upgrade the boiler control systems to assure steam availability. Modern controls are more reliable and can be readily adjusts to load swings caused by varying plant operations.
September 23, Why need boiler controls? 2.Reduce flue gas emissions Failure to comply with the current emissions regulations can be as costly as loss of utilities. Government mandates are enforced by fines, threat of closure, or imprisonment will provide sufficient incentives for plants to comply with the regulations; thus, modernize controls are necessary. Improved in combustion efficiency means reduction in waste disposal problems. And by accurately controlling the oxygen, fuel flow and stack temperature, you will see reductions in plant emissions.
September 23, Why need boiler controls? 3.Maintain boiler safety Modernize control system will have tight integration with flame safety or burner management system to improve safety. Accessing field data, diagnostics functions and alarms can be achieved by coupling modern electronic controls. Password security of the configuration software also assures no unintended changes can be done which can endanger your personnel and equipment.
September 23, Why need boiler controls? 4.Control operating costs a)Reduction in fuel consumption b)Reduction in engineering, installation and startup costs c)Reduction maintenance costs associated with older equipment a)Reduction manpower with automatic responds b)Provide a flexible control strategy to reduce process upsets c)Readily data available for remote monitoring to determine process optimization, boiler efficiency and load allocations
September 23, Combustion control for boilers. Burner combustion control generally includes one or a combination of the following methods:- Excess air regulation Oxygen trim Burner modulation Air/Fuel cross-limiting Total heat control
September 23, Combustion control for boilers. 1.Excess air regulation In actual practice, gas, oil, coal burning and other systems do not do a a perfect job of mixing the fuel and air even under the best achievable conditions. Additionally, complete mixing may be a lengthy process. To ensure complete combustion and reduce heat loss, excess air has to be kept within suitable range. The regulation of excess air provides:- A better boilers hear transfer rate An advance warming of flue gas problems Excess air coming out of the zone of maximum efficiently Substantial savings on fuel
September 23, Combustion control for boilers. 1.Excess air regulation
September 23, Combustion control for boilers. 2.Oxygen trim When a measurement of oxygen in the flue gas is available, the combustion control mechanism can be vastly improved (since the percentage of oxygen in flue is closely related to the amount of excess air) by adding an oxygen trim control module, allowing Tighter control of excess air to oxygen setpoint for better efficiency Faster return to setpoint following disturbances Tighter control over flue emissions Compliance with emission standards Easy incorporation of carbon monoxide or capacity override
September 23, Combustion control for boilers. 2.Oxygen trim
September 23, Combustion control for boilers. 3.Burner modulation Modulating control is a basic improvement in controlling combustion. A continuous control signal is generated by a controller monitoring the steam or hot water line. Reductions in steam pressure or hot water temperature lead to an increase in firing rate. The advantages of introducing burner modulation in combustion control include. Fuel and air requirements are continuously matched to the combustion demand Steam pressure or hot water temperature is maintained within closer tolerances Greater boiler efficiency Weighted average flue gas temperature is lower
September 23, Combustion control for boilers. 4.Air/Fuel cross-limiting A cross limiting combustion control strategy ensures that there can never be a dangerous ration of air and fuel within a combustion process. This is implemented by always raising the air flow before allowing the fuel flow to increase or by lowering the fuel flow before allowing the air flow to drop. Cross-limiting combustion control is highly effective and can easily provide the followings Optimization of fuel consumption Safer operating condition by reducing risk of explosion Fast adaptation to variation in fuel and air supplies Satisfaction of the plant demand fore steam
September 23, Combustion control for boilers. 4.Air/Fuel cross-limiting
September 23, Combustion control for boilers. 5.Total heat control A cross limiting combustion control strategy ensures that there can never be a dangerous ration of air and fuel within a combustion process. This is implemented by always raising the air flow before allowing the fuel flow to increase or by lowering the fuel flow before allowing the air flow to drop.
September 23, Combustion control for boilers. 5.Total heat control
September 23, Fujis oxygen gas analyzer. Top class performance zirconia oxygen analyzer
September 23, Fujis oxygen gas analyzer. Accurate O 2 Measurement is Essential for Energy Saving! The oxygen analyzer consists of a compact zirconia detector that can be inserted directly in wall of the flowing sample gas. The detector measures the oxygen content in the flowing sample gas and transmits the signal to the converter. The converter will then trigger the ON-OFF alarm based on the preset oxygen concentration and give control signal to other devices. Fuji Electrics oxygen analyzer has a unique construction that eliminates the necessity of aspirating sampling gas or injecting air. And make it extremely suitable for monitoring and controlling combustion system like, heater boiler, kiln, melting furnace, low oxygen warehouse and food packing machine.
September 23, Fujis oxygen gas analyzer. Excess air coefficient and energy loss ratio Excess Air Coefficient Exhaust Oxygen, O2 (%) Energy Loss Ratio, Exhaust Gas (%) (In the case of heavy oil combustion at exhaust gas temperature of 250 °C and atmospheric temperature of 20 °C)
September 23, Fujis oxygen gas analyzer. Calculation of cost saving with improved combustion efficiency (The data may varies based on the construction and performance of the boilers) ItemCase 1Case 2 Evaporation rate from boiler5ton/hr1ton/hr Annual operating hours2,000hrs Evaporation multiplier factor for boiler12 Improved value of excessive air coefficient1.6 -> 1.2 (O2 gas from 7.9% -> 3.5%) Kerosene priceUSD 1.05/kg (USD 0.82/, SG 0.78) Kerosene consumption rate5,000kg/hr ÷ 12 = 420kg/hr2,000kg/hr ÷ 12 = 85kg/hr Annual saving through the improved combustion efficiency 420kg/hr x USD 1.05/kg x (13.7 – 10.3) % x 2,000hrs = USD 29, kg/hr x USD 1.05/kg x (13.7 – 10.3) % x 2,000hrs = USD 6, Note: The data shown in the above table are calculated on an assumption of improvement of energy loss = full reduction ratio, therefore the combustion efficiency of the boiler must be taken into account for calculating fuel reduction rate accurately. Fuel reduction ratio will therefore be least several percent higher in actuality.
September 23, Fujis oxygen gas analyzer. Advantages: 1.No sampling device is required The instrument requires no gas aspirating pump or ejector for normal measurements; therefore it can be operated easily. It can be used very conveniently like traditional thermocouple. 2.Compact and light weight design The detector and converter weigh about 1.6kg and 3.5kg respectively. 3.Instrument equipped with indicator and transmitting function The converter is equipped with an indicator that permits direct readout of the oxygen concentration transmitting output function or RS485 communication. 4.Alarm and control functions available Though compact it is compact and lightweight in design, the converter consists of an oxygen concentration setting mechanism as well as alarm setting and control circuits that can transmit control signals. 5.Lost cost Comparing Zircomat-P with other conventional oxygen analyzers it is much more economical in cost. 6.Easy maintenance Zircomat-P assures easier maintenance comparing to other conventional oxygen analyzers and can be used under severe site conditions for a long time.
September 23, Fujis oxygen gas analyzer. System Outline
September 23, Fujis oxygen gas analyzer. Technical Specifications Measuring range0 to 2 ~ 50% RepeatabilityWithin ± 0.5% maximum output signal Linearity± 2% full scale Response timeWith 7 seconds Power Supply100, 115, 220 or 230 Vac, 50/60Hz Power consumption VA Warm up time15minutes Detector TypeDirect insertion type zirconia detector Applicable gas temperature-20~+600 °C or -20~+1,590 °C Sample gas pressure-3~+3kPa (-306~+306mmH2O) Ambient temperature-20~+60 °C or -5~100 °C Converter Output signal4~20mA or 0~1Vdc Indication oxygen concentration3-digits LED Indication operation/settings16-digits LCD Mode display03 x LED MountingPanel or Pipe Mounting Optional functionRS-485
September 23, Fujis oxygen gas analyzer. Standard air ratio by Energy Economy Law in Japan for conservation of energy Based on Article 4, Clause 1 of the law regarding rational use of energy (Law No. 49 published in 1979), judging standard for enterprisers at factories (Notification No. 467 of the Ministry of Commerce and Industry, dated October 1979) has been amended on October 26, 1979 (Notification No. 559 of the Ministry of Commerce and Industry) to specify standard air ratio. ClassificationLoad Ratio (%) Standard air ratio Solid Fuel Liquid fuel Gaseous fuel Blast furnace gas For electrical enterprise75~1001.2~ ~ Others Evaporation rate exceeding 30ton/hr 75~1001.2~1.31.1~ Evaporation rate from 10~30ton/hr 75~ ~1.3 - Evaporation rate not exceeding 10ton/hr 75~ Boilers
September 23, Fujis oxygen gas analyzer. 2. Industrial Furnaces ClassificationStandard air Ratio Metal melting furnace1.3 Continuous steel heating furnace1.25 Metal heating furnace not continuous steel heating type1.3 Continuous thermal treatment furnace1.3 Gas producer and gas heating furnace1.4 Oil heating furnace1.4 Pyrolytic furnace and modification furnace1.3 Cement kiln1.3 Alumina kiln and lime kiln1.4 Continuous glass melting kiln1.3