General Description of Boiler
Two-drum type steam generator is field-erected unit designed to meet the requirement of industry for increased reliability and comparatively site construction. The features of the unit are as follows:
Drum shells will be made of steel plates A516 All seams will be welded, examined x-rayed and stress relieved as per EN-12952 Drum will be provided with manhole opening on either end. All nozzles will be welded to the drums and provided with cover plates; drum will be fitted with an internal feed pipe for proper distribution of feed water, internal pipe for blow down, chemical injection pipe and steam purification equipment (separators & driers).
Furnace will be completely surrounded by welded finned water tube walls. This construction has the following outstanding features:
Every wall tube will be secured to drums by expanded joints.
We will design the outer casing to cover the exterior of boiler. Three (3) inspection openings will be considered & designed for the surveillance of combustion in the furnace. They should be equipped with sealing air piping, in order to prevent furnace gas from coming out when openings are opened during boiler operation. Steam and water drum, boiler casing, ducts and piping will be so designed that the suitable insulation can be applicable.
Special shaped fire brick, insulation materials (Rockwool blanket, Calcium silicate, hard cement) and other setting materials required for the boilers will be furnished by us.
Steel Structures, Platforms, Walkways and Stairs
We will design all platforms, safety ladders, walkways, stairs, and hand railing required for normal access and inspection of equipment.
One forced draft fan per each boiler is considered which should equip with the driving motor. The F. D. Fan is sized to provide margins of 10% and 21%, respectively, for air flow and pressure over the requirements at MCR condition.* 10% Excess air is included in the requirement of MCR condition for fuel Gas respectively.
Fuel burning equipment
The boiler is designed to equip for using Fuel gas as main fuel, as shown in attached P&ID. Fuel gas system should be equipped with relevant valve racks as well as shown in P&ID. Boiler has two burners designed to burn the Fuel gas.
General Description of Control and Instrumentation
A complete set of field instruments as shown in attached P&I diagram and the control system
described herein should be provided. The boiler will be controlled by PLC. The PLC hardware will be located in auxiliary room and related peripherals such as operator consoles printer, PLC will be located in control room. We will design the complete control system for start up running and protection of boiler to achieve a suitable and reliable operation of the boiler. The control system will consist of the following sub-systems:
- Automatic Boiler Control system and supervisory
- Burner Management System and Boiler Safety Interlocks
- Auxiliary Equipment control system
Automatic boiler control system
This system will be designed in such a way that the boiler be capable to cope with load changes in maximum rate of 5 percent of MCR per minute either felt through boiler master or caused manually by operator. This system will be composed of the following sub-systems:
The automatic boiler control range is 30% to 100% MCR Load.
Master control system
This system will be designed in order to maintain the steam pressure at a substantially constant level by regulating the load demand signal to the boiler in response to changes in the measured steam header pressure.
Combustion control system
The duty of this system is regulating of fuel and combustion air flows introduced in the furnace
Depending on the signal generated by the master control system, in such a way that no risk of
Explosion will occur in the furnace and at the same time combustion takes place with a maximum efficiency. The combustion airflow should be trimmed by O2 % signal measured by an O2 analyzer in boiler outlet flue gas. Moreover, the combustion control has the function of air rich control during load up and load down.
Feed water control system
This control system will be designed as three elements type, in that three process variables, steam flow, feed water flow and drum level, are used as inputs to the control loop that regulates feed water flow to the drum to maintain the drum level at set point. This is a cascade feed forward loop with drum level as the primary variable, steam flow as the feed forward input, and feed water flow (feedback) as the secondary variable.
Steam temperature control
Saturated steam temp. Control with press. Of steam drum.
Boiler monitoring system
Boiler monitoring/supervisory will be designed via operator consoles. The following variables will be recorded and indicated in the control room:
Auxiliary equipment control system
This control system shall include the control & supervisory of the soot blowers. For soot blowers a separate PLC will be provided. (If required) boiler has only for soot blowers (optional).
Boiler control panel
We will design one local control panel to be installed in the boiler area for each boiler. The panel should be fully assembled & wired up to terminal blocks and weatherproof. Each panel will include indicators for necessary and major variables such as drum level, etc. This panel will also include push button indication lights for start and shut down the burners.
We will design all necessary field instruments within the scope as shown on attached P&ID diagram. Instruments include following items and will be provided with necessary valves, accessories and installation materials.
- Transmitters (If required)
- I/P converters
- Actuators & positioner for control drives
- Pressure, and level switches or monitor switches
- Pressure, temperature, and level gauges
- Level gauge for steam drum
Classified area, except the instruments attached to the burner (i.e. flame detectors) and mounted on the
Gas lines which will be of explosion proof type.
The provided electrical systems and equipment will be as the following if required:
- MCC and small power distribution panel 0.4 kV.
- Motors local push buttons and indication lights.
- Power, instrumentation, and control cable within battery limit
- Cable glands and cable trays within the scope
- Earthing wires & materials inside the battery limit
- 6 kv starter units for FDF motors. (If required)