Application of sequence control in domestic 450th

2022-06-10
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Application of sequential control in domestic 450 t/h CFB boiler

Abstract: This paper introduces the application of sequential control system (SCS) in CFB boiler, and analyzes the sequential control logic of CFB boiler of 125MW Unit in the technical transformation project of Baoding thermal power plant

key words: CFB boiler; Sequence control; Logical structure

1 overview

technical transformation project of Baoding thermal power plant 2 × The boiler of 125MW Unit #8 unit adopts DG450/9 Type CFB boiler is the first million kilowatt power station CFB Boiler in China burning coal with a market value of poor global advanced polymer composites or US $12.12 billion, which is developed by Oriental Boiler Co., Ltd. (DBC) on the basis of introducing the large CFB boiler technology of Foster Wheeler (FW) Company in the United States. It adopts the combustion mode of fly ash recirculation, which can not only increase the adaptability of boiler combustion to fuel, but also improve the combustion efficiency of boiler, increase the furnace heat load of boiler, improve the utilization efficiency of desulfurizer, further reduce the emission of no and expand the load regulation range of boiler. The supporting steam turbine adopts CC 83/0.98/0.196 single shaft, double cylinder and two exhaust, high pressure, reaction type, 100MW double extraction condensing steam turbine. The sequence control system (hereinafter referred to as SCS) in the thermal control system (DCS) is a part of XDPS-400 distributed control system. XDPS-400 distributed control system also includes analog control system (MCS), burner management system (BMS), data acquisition system (DAS), steam turbine electro-hydraulic control system (DEH) and electrical quantity control system (ECS). The data highway is used for data communication between systems, and the hardware redundancy configuration is also used for individual important signal acquisition. The interlocking between main protections is connected by hard wire to ensure the reliability of system operation

the main auxiliary equipment of #8 unit CFB Boiler in Baoding thermal power plant technical transformation project includes 2 induced draft fans, 2 primary fans, 2 secondary fans, 2 coal sowing fans, 2 J-Valve fans and 1 ignition booster fan

2 function and composition of SCS

2.1 function

SCS is mainly used for automatic start and stop operation of main and auxiliary machines and operation of local process flow in thermal system. According to the needs and characteristics of each process flow and the requirements of predetermined process sequence, sequence and logic conditions, it makes the equipment and auxiliary facilities in the production process automatically carry out a series of operations in turn. The use of the system can effectively prevent equipment failure or system failure caused by misoperation

sequence control is the logic control of starting or stopping the system composed of the main equipment to be started and relevant auxiliary equipment. It executes sequence control logic centered on one main power equipment or important system equipment, such as induced draft fan start and stop subgroup, primary fan start and stop subgroup, secondary fan start and stop subgroup, electric feed pump start and stop subgroup, high-pressure heater switching subgroup, etc. Taking the electric feed pump as an example, the sequence control sub group includes the control of electric feed pump motor, auxiliary oil pump, outlet electric valve, recirculation valve and other related equipment, which is mainly used to automatically realize the functions of starting and paralleling of auxiliary machines, stopping and exiting the system of auxiliary machines. The sequence control system of each subgroup can be operated independently, which is very convenient and shortens the start and stop time of the unit

XDPS distributed control system provides step logic function module to realize sequential logic control. In the unit, forced draft fan (including forced draft fan, guide vane and outlet baffle), air preheater (including main motor of air preheater, primary and secondary air valves and flue gas inlet valve), induced draft fan (including induced draft fan, guide vane and outlet baffle), primary fan (including primary fan, guide vane and outlet baffle), electric feed pump (including electric feed pump, booster pump, electric pump auxiliary oil pump and outlet valve) The high-pressure heater (including feed water inlet and outlet valves, extraction isolation valves, check valves and high-pressure heater drain valves) adopts sequential logic control

2.2 constitute

SCS of #8 and #9 units of Baoding thermal power plant technical transformation project, including subgroup level sequence control and equipment level control

subgroup level sequence control is to control an auxiliary machine and its auxiliary equipment as a whole. In order to reduce the operating burden of operators and shorten the start-up and shutdown time of the unit, the sub group level sequence control is designed to automatically complete the start-up and parallel of auxiliary machines or the shutdown and out of system of auxiliary machines. The start and stop of each sequence control sub group can be operated independently. Through CRT, the system flow chart of each sub functional group and related equipment can be displayed, including equipment status, operation mode, allowable conditions, operation sequence and next action, as well as the operation sequence description and operation guidance of manual start and stop operation of auxiliary equipment. The sub group level sequence control fully considers the safety protection conditions of auxiliary equipment, and can display important auxiliary tripping conditions on the CRT screen

equipment level (drive level) control includes the basic control circuit and interlocking protection logic of a single equipment. Each controlled equipment entering the sequence control system can be operated by the sequence control command of the upper level or by the operator on the CRT

the main subgroup controls are:

A. boiler side: induced draft fan subgroup, primary air fan subgroup, secondary air fan subgroup, J valve fan subgroup, coal sowing fan subgroup, ignition booster fan subgroup, limestone powder feeding fan subgroup and coal feeder control subgroup

B. steam turbine side: electric feed pump control subgroup, high pressure heater subgroup, low pressure heater subgroup, condensate pump subgroup and water jet pump subgroup

C. electrical side: generator and sub group

the step algorithm of the special step sequence logic module in XDPS-400 distributed control system defines the standard implementation method of sub group level sequence control. Its main functions are: start, stop and end of step sequence logic; Override of step sequence logic (protection condition); Permission of step sequence logic (locking condition); Set relevant equipment as sequence control mode; Automatic progress after step sequence action is completed; Suspension of step sequence in case of failure; The step sequence expires; The operator jumps and sets the steps; Step status and step operation time display; Step sequence fault display and operation guidance

The execution of

step sequence is both conditionally triggered and time-based. After the operation of the current step is successful (the feedback signal reaches or reaches the set time), the program automatically proceeds to the next step. If the fault does not disappear after a certain time delay or the step sequence setting time operation is not completed, the step sequence logic will be suspended. After the sequence control logic is started, the operator can manually stop the program or choose to skip or set the step at any time. Step skipping and step setting operations can only be performed when the equipment safety conditions are met

3 step sequence process of sequence control subgroup

the following describes the step sequence process of sequence control subgroup with primary air fan and secondary air fan

3.1 sequence control subgroup of primary air fan

3.1.1 allowable starting conditions

allowable starting conditions are: establishment of air passage; Any one J-Valve fan operates; No tripping condition of primary air fan exists; Any one induced draft fan operates

If the inlet and outlet baffles of the primary fan have been switched on in step P <1.3 and the other one has been switched on

Step 2: start the primary air fan motor

Step 3: delay 30s, open the outlet baffle of primary air fan and release the inlet regulating baffle

Step 4: close the inlet and outlet baffles of another primary air fan (if another primary air fan has been running, skip this step)

3.1.3 stop steps of primary air fan

Step 1: close the inlet baffle of primary air fan

Step 2: stop the primary air fan motor

Step 3: delay 30s and close the outlet baffle of primary air fan

3.2 sequence control subgroup of secondary air fan

3.2.1 allowable starting conditions: establishment of air passage; Any one J-Valve fan operates; No tripping condition of secondary air fan exists; Any induced draft fan operates

3.2.2 starting steps of secondary air fan

Step 1: close the outlet and inlet baffles of secondary air fan (if another secondary air fan has been running and the inlet and outlet baffles have been opened, skip this step)

Step 2: start the secondary fan motor

Step 3: delay 30s, open the outlet baffle of secondary fan and release the inlet regulating baffle

Step 4: close the inlet and outlet baffles of another secondary fan (if another secondary fan has been running, skip this step)

3.2.3 stop sequence of secondary air fan

less than half a year

Step 1: close the inlet baffle of secondary air fan

Step 2: stop the secondary fan motor

Step 3: delay 30s and close the outlet baffle of secondary fan

4 main protection (MFT) related to SCS in CFB boiler

when any of the following conditions are met, the boiler will cut off all fuel and MFT protection will act to extinguish the furnace

A. manual MFT (press two MFT buttons on CRT console at the same time)

B. the average bed temperature is greater than 990 ℃

C. the switch action of high furnace pressure (+ 2489pa) is delayed for 5S

D. switch action of low furnace pressure (- 2489pa), after 5S delay

E. high two value (+ 125mmh2o) and high three value (+ 200mmh2o) signals of drum water level exist at the same time

F. low binary (- 150mmh2o) and low ternary (- 280mmh2o) signals of drum water level exist at the same time

g. two induced draft fans trip (zs1401a, zs1401b)

h. two primary fans trip (zs1103a, zs1103b)

I. two secondary fans trip (zs1203a, zs1203b)

J. two J-Valve fans trip (zs1301a, zs1301b)

K. the inlet air volume (standard air volume) of the primary fan is less than 25% of the total air volume, with a delay of 5S

Jinan new era Gold Testing Instrument Co., Ltd. welcome to consult our products. L. the average bed temperature (upper layer) is less than 650 ℃ and the ignition oil gun of the air duct under the bed is not put into operation

M. the material level of any cyclone is high (local switch action), with a delay of 5S

n. all coal feeding booster fans are shut down and the bypass valve is not opened

O. the main throttle valve of the steam turbine is closed

P. it exceeds the start-up time (3600s)

5 Conclusion

with the continuous improvement of the automation level of the thermal control system, the sequence control system has also been further developed. The sequence control function is no longer limited to the simple step-by-step operation of equipment startup and shutdown, but has developed into step-by-step control, interlocking protection Dynamic test and other multi-functional integrated control system. The application of sequence control system in Baoding thermal power plant #8 and #9 CFB units reduces the working intensity of operators and the possibility of misoperation. From the beginning of commissioning to the production and operation of the unit, all functional groups have been put into operation, and the input rate of interlocking protection has reached 100%, which plays a role in ensuring the economic and efficient production of the unit

references

[1] Wang Hao Design of circulating fluidized bed boiler control system in Aixi power plant [J] Thermal automation of thermal power plant, 2000, (4) (end)

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