Document code: 1 (10) Project : MULTI FUEL CFB BOILER SIMULATOR Author: Approved: Language: JJA Document title: SYSTEM DESCRIPTION DUCT BURNERS Submitted for: Customer reference: Other information:
Document Code: 2 (10) TABLE OF CONTENTS 1 GENERAL... 3 2 DESIGN DATA... 4 2.1 Duct burner... 4 2.1.1 Fuels... 4 2.1.2 Atomizing medium... 4 2.1.3 Combustion air... 4 2.2 Igniter... 4 2.2.1 Fuel... 4 2.2.2 Air... 5 2.2.3 Supply voltage... 5 3 EQUIPMENT DATA... 5 3.1 Duct burners... 5 3.2 Type of nozzle... 5 3.3 Valve set for burners... 5 3.4 Oil... 5 3.5 Purging air... 6 3.6 Atomizing air... 6 3.7 Ignition gas... 6 3.8 Instrument air... 6 3.9 Flame monitors... 6 3.10 Ignition burner... 7 4 AUTOMATION AND INSTRUMATION... 7 4.1 General... 7 4.2 System control... 7 4.2.1 Starting the PURGE... 7 4.2.2 Duct burners basic logic... 8 4.3 Fuel oil flow control... 8 4.4 Fuel oil pressure control... 9 4.5 Minimum oil flow... 9 4.6 Measurements... 9 4.7 Interlocking... 9 5 CONNECTED SYSTEMS... 10 6 APPENDICES... 10
Document Code: 3 (10) 1 GENERAL The function of the duct burner is raise the temperature of the primary air and in that way support start-up burners bring the bed temperature up with to the permissible peat ignition temperature. Equipments which are included in the system are introduced in P&I -diagrams S1 HHA -MFB0001 Duct burners are located in the primary air duct. Burners are normal air atomizing (plant air) oil burners completed with a burner management control and safety system. Propane / butane gas is used as ignition gas. Pressurized air is used as atomizing medium, the pneumatic valves and cylinders are controlled by means of instrument air. Main combustion air for the burners is hot primary air. Intrex air supply is for cooling air of flame scanners and combustion air for the igniters. During startup, the boiler must be uniformly heated so that the parts are not damaged by thermal stress. The burners must be started and the primary air duct slowly brought up to a temperature that will allow safe level (below 400 C). Maximum load of the one duct burner is approx. 4 MW with control ratio 1:4. This provides about 8 MW duct burners heat input to the boiler. There are two duct burners on primary air duct. The initial setpoint for feeding of solid fuel will be greater than 500 C and one start-up burner must be in use. Once peat is ignited and the bed temperature is greater than 600 C, the burners can be taken out of service. All duct burner valve racks are identical. The main components of the valve rack are two main fuel oil safety shut-off valves, two ignition gas shut-off valves, one ignition gas ventilation valve, clean purging valve, safety shut-off valves and one atomizing purge valve, four manual isolation valves for the instrument air, fuel oil, ignition gas and atomizing pressure air and two non-return valves for atomizing and clean purging. Ignition gas and instrument air lines are equipped with strainers. Connection between the valve racks and burners is carry out by the flexible metal hoses, which allow the thermal movement of the burner without putting stress to the piping of the valve racks. Each duct burner valve rack has a local control panel with a flame detector signal amplifier and flame intensity meter. From the local operating panel it is possible to start and stop the burner sequence program through commands from the Distributed Control System. The local panel functions as termination panel for a burner and valve train electrical devices and instruments. The burner assembly consists of a burner register and windbox, front plate with inspection sight glass, retractable lance with extended and retracted limit switches, impeller, main fuel lance coupled switch, two flame detectors, gas igniter and igniter high voltage transformer package for spark initiation. A small quantity of intrex air are used to provide purging, sealing and cooling for the burner assembly. Each duct burner has a refractory hood which protects the immediate primary air ducts from excessive heat and gives shape and a direction to the ignition flame.
Document Code: 4 (10) 2 DESIGN DATA As a design basis for the duct burner system are the following data. 2.1 Duct burner 2.1.1 Fuels Quality: Light fuel oil Capacity: max. 300 kg/h oil Temperature: 30 C Oil supply pressure: 16 bar 2.1.2 Atomizing medium Quality: Consumption: Pressure: plant air 30 kg/h 6 bar 2.1.3 Combustion air Quantity: 3450 Nm 3 /h Continuous flow: 3450 Nm 3 /h Pressure: 0,2 bar Temperature: 20 200 C 2.2 Igniter Length L=1150 2.2.1 Fuel Quality: LPG Consumption: 13,5 Nm 3 /h Supply pressure: 0,5..1,5 bar
Document Code: 5 (10) 2.2.2 Air Quality: HP air Consumption: 270 Nm 3 /h Supply pressure: 0,4 bar 2.2.3 Supply voltage Voltage: 8,5 kv 3 EQUIPMENT DATA 3.1 Duct burners Manufacturer Foster Wheeler Energia Oy KKS numbers S1 HHA10/20 AV101 Capacity: max. 300 kg/h oil each Oil supply pressure: 16 bar Control ratio: 1:4 3.2 Type of nozzle WD 6 22, 80, WD 5 13, 80 6 = number of holes 22 = hole diameter (2.2 mm) 80 = angle of holes (WD = type) See also manufacturer's instructions. 3.3 Valve set for burners Each start-up burner has its own valve set consisting of the following items. 3.4 Oil Manual shut-off valve with limit switch for oil Oil quick shut-off valves (2 pieces) Pressure gauge for oil
Document Code: 6 (10) 3.5 Purging air Manual shut-off valve for purging air Purging air quick shut-off valve Pressure switch for purging air Back pressure valve for purging air 3.6 Atomizing air Manual shut-off valve for atomizing air Atomizing air quick shut-off valve Pressure gauge for atomizing air Pressure switch for atomizing air Back pressure valve for atomizing air 3.7 Ignition gas Manual shut-off valve for ignition gas Electric quick shut off valves (3 pieces) Filter for ignition gas 3.8 Instrument air Manual shut-off valve Filter for instrument air Solenoid valve group: For quick shut-off valve of atomizing air For first shut-off valve of purging air For second quick shut-off valve of purging air For first quick shut-off valve of oil For second quick shut-off valve of oil Throttle valve for first quick shut-off valve of oil 3.9 Flame monitors Manufacturer Durag Type Flame sensor D LE603 Type Flame monitor control unit D-UG 660
Document Code: 7 (10) 3.10 Ignition burner Manufacturer Foster Wheeler 4 AUTOMATION AND INSTRUMATION 4.1 General Bed will be heated by duct and start-up burners during start-up and firing of a low-grade solid fuel, which is not capable to keep bed temperatures high enough. The effect of the duct burners will be controlled by altering the oil flow rate. There are two different ways to control start-up burners: oil pressure control oil flow control. Pressure control must be used when starting the first burner. The other burner can be started by using flow control. Control mode will be chosen by setting the desired controller in automatic mode. Now the controller that has been earlier on automatic mode falls off from controlling. For more details of control and function you find from function description of duct burners. 4.2 System control Before starting the first burner, furnace has to be purged if the bed temperature is under 600 C. 4.2.1 Starting the PURGE PURGE can be started on the screen from switch "PURGE", then control loops of secondary air for lower and upper level switches to manual control mode and PURGE logic starts to open the control dampers. When total air flow to the boiler is > 50 % the dampers are locked in their position and PURGE time begins. When furnace has been purged and boiler interlocking is in order, boiler is ready for ignition. Now secondary air controls switch to cascade modes. Boiler is ready for ignition if less than 30 minutes has passed after stopping the PURGE.
Document Code: 8 (10) Duct burners basic logic 4.2.1.1 Duct burner starts according to the following sequence: 1. Booster fan starts and air damper to the ignition position * Pressure difference enough for ignition 2. Atomizing air valve opens * atomizing air pressure > min 3. Ignition transformer on, ignition gas valves open 4. Flame observed 5. Oil shut-off valve of oil opens. * quick-close valves on open limit and flame observed 6. Ignition transformer off, ignition gas valves close * flame observed 7. Air damper to the cascade mode 4.2.1.2 A duct burner stops according to the following sequence 1. Air damper to the ignition position * Pressure difference enough for ignition 2. Ignition transformer on, ignition gas valves open * flame observed 3. Oil Shut-off valve closes, purging air valve open * quick-close valves close and purging air valve open, flame observed 4. Purging air valve closes (30 s purging) * flame observed 5. Ignition transformer off, ignition gas valves close 6. Air damper to the cascade mode * Burner out 7. Atomizing air valve closes. If the duct burner stops because of interlocking without purging, stop sequence must be started manually again after the interlocking has been released. 4.3 Fuel oil flow control When oil control is in pressure control mode, output of this flow control follows output of pressure controller. In that way pressure impulses can be avoided when changing the control mode. Controller has control modes as follows: Manual mode Position of control valve will be controlled manually 0-100% Automatic mode The controller controls constant flow set point.
Document Code: 9 (10) 4.4 Fuel oil pressure control First burner is started by using pressure control mode. The controller ensures that oil pressure will not fall below the minimum level when burners are in use. Controller has control modes as follows: Manual mode Position of control valve will be controlled manually 0-100%. Automatic mode The controller controls constant pressure set point. 4.5 Minimum oil flow Close valve in duct burners oil return line, which closes automatically when oil valves in some duct burner open. Valve opens when oil valves in both burners are closed (hand valve or both quick closing valves). 4.6 Measurements See the automation descriptions. 4.7 Interlocking See the automation descriptions. Burners are ready for use when boiler interlocking are in order and burner is ready for operation (no alarms on).
Document Code: 10 (10) 5 CONNECTED SYSTEMS Flue gas system Primary air system Instrument air distribution in boiler house Pressurized air distribution in boiler house Fuel oil Ignition gas Intrex air S1 HN -MFB0001 S1 HL -MFB0001 S1 QFH -MFB0001 S1 QEH -MFB0001 S1 HJ -MFB0001 S1 HJ -MFB0001 S1 QDA -MFB0001 6 APPENDICES Control- and logic diagrams Duct burner system S1 HHA -MFB0001