Combustion Control System - Full Metered with Oxygen Trim

GENERAL SPECIFICATION

SECTION 15901 CONTROLS AND INSTRUMENTATION (BOILER PLANT)

PART H: REQUIRED CONTROL FUNCTIONALITY

COMBUSTION CONTROL SYSTEM - FULL METERED WITH OXYGEN TRIM

For more information contact:

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MicroMod Automation & Controls, Inc. 75 Town Centre Dr. Rochester, NY 14623 USA Tel. 585-321-9200 Fax 585-321-9291

www.micromod.com H. Required Control Functionality

1. Combustion Control a. The system shall be a full metered cross-limited control system with oxygen trim to maintain main steam header pressure at the selected value. Positioning systems that depend on actuator feedback pots for cross limiting are not acceptable.

b. A single dedicated controller shall be provided which contains the Boiler Master and Fuel Flow control loops. Separate displays shall be provided for each loop. A second dedicated controller shall be provided which contains the Air Flow and Oxygen Trim control loops. Separate displays shall be provided for each.

c. The Boiler Master shall be capable of performing either as a Bias Station, receiving an external Plant Master signal or a Drum Pressure controller comparing measured steam to setpoint and modulating the fuel valves accordingly. Separate characterization tables for gas an oil valves shall be provided.

d. Failure of the plant master shall not affect continued operation of the individual boiler. Provision shall be made for independent operation of the Boiler Master loop if the signal from the Plan Master is no longer available, without reconfiguration of the control strategy. It shall be possible to wire both the Plant Master and Drum Pressure signals to the controller, and for the operator to switch between control strategies from the front panel of the controller provided the Boiler Master loop is in manual, without reconfiguration or rewiring. Automatic bumpless transfer from Manual to Automatic mode shall be provided.

e. The airflow shall be measured, temperature compensated, and sent as a total airflow signal to the Air Flow control loop. The total flow is compared to the air demand setpoint and added as a trim signal to the feedforward for air demand to modulate the air damper. Fuel/air ratio shall be determined by independently characterized setpoint curves for both oil and gas. The Oxygen control loop shall provide a limited adjustment to the Air Flow control loop remote setpoint for the amount of air for the current amount of fuel. Separate characterization tables for load programmed setpoints for oil and gas shall be provided.

f. Cross Limits on fuel and air shall ensure that air increases before fuel on a demand increase, and that fuel decreases before air when demand decreases, guaranteeing sufficient combustion air at all times and preventing a fuel-rich atmosphere. Additionally, the control system shall ensure that fuel demand cannot be increased beyond a certain amount above the measured air flow, and air demand cannot be decreased beyond a certain amount below the measured fuel flow. g. To provide for additional safety and ease of operation the controllers shall have automatic mode switching based on the status of the Air Controller and the BMS. For example, when the Air Controller is placed in Manual (MAN) mode the fuel controller shall be automatically switched to Manual, the Boiler Master shall track total fuel percentage and the Oxygen Trim controller shall track a constant value. All controllers shall reject to Manual mode on bad signal quality. h. When the fan is equipped with both a damper and a Variable Frequency Drive, the demand for air provides a signal to the pre-programmed positions for the fan VFD and damper that are located in separate characterization tables for oil or gas. The fan operates in a split range control mode with the damper controlling flow at low loads and the VFD controlling flow at high loads. i. A logic interface to the BMS shall be provided where a contact closure will position the fuel valves to a pre-programmed light off position. The controllers shall also contain logic to prevent fuel automation until the airflow is automated. j. All loops shall be capable of complete local operation and visualization via dedicated displays. If the controllers are connected to a computer console or operator interface panel for normal operation, failure of the console or panel shall not deprive operations personnel of the ability to visualize and run the boiler in manual or automatic with full control of all functions. k. Measured fuel flow as well as shift and continuous totals for each fuel shall be indicated, with the provision to clear shift totals from the front panel. l. It shall be possible to enter coordinates for fuel-air ratio setpoint curves and valve characterization tables from the front panel of the controller if desired, without requirement for a separate configuration or tuning device of any type. Combustion and characterization tables shall provide capacity for a minimum of 10 x,y pairs per table. m. An option shall be provided for calculation and display of real time boiler efficiency to be calculated using the Heat Loss method, and displayed on the controller front panel along with current stack temperature. A flue gas temperature transmitter must be provided and installed at the boiler outlet. n. An option for Flue Gas Recirculation (FGR) control shall available where the demand for air provides a signal to the pre-programmed positions for the FGR damper. Separate characterization tables for oil and gas shall be provided. The operator may provide a manual FGR position in manual mode. o. Options shall not be mutually exclusive and shall be capable of being enabled from the front panel of the controller without reconfiguration of the control strategy, provided the required I/O is installed. It shall be possible to add optional I/O in the field at any time and have it automatically recognized once the option is enabled. p. Boiler-specific documentation that clearly explains system installation, setup, startup and operation of the controller for combustion control shall be provided. Generic controller installation, configuration and operation manuals shall not be acceptable. q. All inputs and outputs shall be galvanically and optically isolated such that a failure of one I/O point shall not cause failure of any other. r. Communication via RS-485 Modbus RTU for connection to a computer or operator panel shall be included as standard. s. Controllers shall carry a 2-year warranty after date of shipment. t. The system shall be factory manufactured and tested according to FM/CSA Class 1, Division 2, Groups A,B,C,D. The control system shall be a MicroMod Automation, Rochester NY, MeterPAK combustion control system.