CN111871169A

CN111871169A - Control method for solving problem of inverted suspension of Nox signal of coal-fired boiler in thermal power plant

Info

Publication number: CN111871169A
Application number: CN202010708193.1A
Authority: CN
Inventors: 高利斌
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-07-16
Filing date: 2020-07-16
Publication date: 2020-11-03

Abstract

According to the current problem of inverse hanging of flue gas NOx signals of a denitration control system commonly existing in some thermal power plant boilers in China, the control method utilizes the installation equipment of the existing boiler denitration control system and the DCS control system according to the flowing characteristic of flue gas as fluid and the working principle of measurement and installation of a thermal instrument sensor, under the condition of not increasing equipment and investment, the problem of inverse hanging of the clean flue gas Nox signal of the thermal power plant coal-fired boiler, which is greater than the flue gas Nox signal of a desulfuration inlet, and the flue gas Nox signal of the desulfuration inlet, which is greater than the outlet Nox signal of a denitration device, is solved by comprehensively analyzing the relevant data of the DCS control system and reasonably distributing and adjusting the ammonia injection quantity of each nozzle, so that the automatic control level of the denitration system is improved, the ammonia injection quantity of the denitration device outlet matched with load is controlled as well as possible in different stages of load, and the purposes of energy conservation and, and more solution benefits are created for enterprises.

Description

Control method for solving problem of inverted suspension of Nox signal of coal-fired boiler in thermal power plant

A technical field

The invention relates to a control method for solving the problem of inverted hanging of Nox signals of a coal-fired boiler of a thermal power plant, which is particularly suitable for a large-scale coal-fired boiler of the thermal power plant with an SCR (selective catalytic reduction) denitration device adopting a plurality of nozzles.

Second, background Art

At present, with the further improvement of national requirements on energy conservation and emission reduction, a denitration device is required to be installed on a large-scale thermal power plant coal-fired unit, the emission standard of clean flue gas NOx of the denitration device is required to be less than 50mg/Nm3, the denitration device is installed in a rectangular flat flue between an outlet of a boiler economizer and an inlet baffle of an air preheater, a reactor containing a catalyst is installed inside the denitration device, a denitration outlet NOx measuring device is installed on a horizontal flue behind the inlet baffle of the air preheater, a desulfurization inlet flue gas NOx measuring device is installed on the horizontal flue after outlets of two induced draft fans are connected together, and a clean flue gas NOx measuring device discharged from an outlet of a chimney is installed in the horizontal flue from a rear part of a wet dust collector to the chimney.

The denitration principle is that after air and ammonia in dilution air are mixed by a mixing device, the diluted ammonia is sprayed into an SCR denitration device through a plurality of nozzles controlled by a manual door, the diluted ammonia sprayed by the nozzles is mixed with flue gas, and nitrogen oxide and the ammonia and oxygen are subjected to chemical reaction to generate nitrogen and water under the action of a catalyst, so that the effect of removing the nitrogen oxide in the flue gas, commonly called denitration, is achieved.

Because the denitration device is a rectangular structure, the inlet flue gas flue of the air preheater is a flue which is similar to a square, and the shape of the flue gas is changed to a certain extent, the flue gas sampling measurement is carried out at the central part of the horizontal flue from the aspect of the reliability of the flue gas measurement, the flue gas sampling measurement has certain representativeness, and from the use condition of the prior boiler denitration control system in China, because the problem that NOx signals are hung upside down, namely NOx of clean flue gas is larger than that of the flue gas at the desulfuration inlet, NOx of the flue gas at the desulfuration inlet is larger than that of the outlet of the denitration device, and the automatic regulation and control of the denitration system are not ideal, the intelligent ammonia injection control, also called as an accurate ammonia injection control system, is developed by manufacturers by utilizing the technologies of prediction algorithm, fuzzy control and the like in the aspect of computer control, and is used for the improvement of the boiler denitration control system of a thermal power plant so as to meet the purposes of meeting the environmental, however, due to the design, the position of the measuring point, the installation and other reasons, the regulating valve and the measuring point signal are difficult to correspond one to one, so that accurate ammonia injection control cannot be achieved, and if the problem of signal hang-over is not solved, the aims of meeting the environmental protection requirement and reducing the ammonia injection amount are difficult to achieve.

The invention is developed aiming at the situation, fully utilizes the flowing characteristic of the flue gas and the automatic measuring principle of the thermal process, and reasonably adjusts the ammonia injection amount of each nozzle in a manual mode to solve the problem of the inverse suspension of NOx signals in the flue gas system measurement of the power station boiler so as to solve the requirement of denitration on the measuring signals automatically.

Third, the invention

In order to overcome the defects of the background art, the invention provides a control method for solving the problem of inverted suspension of Nox signals of a coal-fired boiler in a thermal power plant, which aims to solve the problem of long-term inverted suspension of NOx measurement signals of a boiler denitration system, namely: the clean flue gas Nox signal is greater than the desulfurization inlet flue gas Nox signal, and the desulfurization inlet flue gas Nox signal is greater than the condition of NOx at the denitration outlet, so that the automatic regulation and control of the denitration system are facilitated, the environmental protection requirement is met, and the NOx emission is prevented from exceeding the standard and being checked.

The control principle adopted by the invention is based on the following steps: the flue gas flowing in the flue has a high flue gas flowing speed at the central part of the flue, and the flowing speed of the flue gas at the periphery of the flue is relatively low, so that the flue gas extracted from the central part of the flue has certain representativeness in measuring and analyzing NOx, and because the denitration outlet is far away from the flue gas at the desulfuration inlet, the flue gas at the desulfuration inlet has a certain distance from the clean flue gas, so that three NOx measuring signals have certain hysteresis, and under the condition that a unit is loaded with certain denitration ammonia injection amount, the NOx of the clean flue gas is always smaller than the NOx of the flue gas at the desulfuration inlet by about 10mg/Nm3 through manual adjustment, thereby solving the problem of the inverse hanging of the NOx signals.

A control method for solving the problem of the inverted suspension of Nox signals of a coal-fired boiler in a thermal power plant is characterized by comprising the following steps: the diluted ammonia gas is reasonably distributed to each nozzle through manual door control adjustment, the nozzles with large influence on NOx signals at the denitration outlet adopt a less-spraying control mode, so that the smoke NOx signals at the denitration outlet are controlled to be larger than those at the desulfuration inlet, and the smoke NOx signals at the desulfuration inlet are larger than those of clean smoke NOx.

The specific mode is as follows: firstly, a primary door in front of a nozzle is completely opened to the maximum, then the nozzle in the middle of the denitration device is closed to be small, and then the denitration device is repeatedly adjusted according to numerical values of outlet flue gas NOx, desulfurization inlet flue gas NOx and clean flue gas Nox of the denitration system until the denitration device meets the requirements. Such as: if the influence of the middle nozzle is large, the middle nozzle is closed, so that the opening of the primary opening in front of the denitration system nozzle is in a V-shaped shape, namely, the opening of the two sides is gradually reduced towards the middle in an adjusting mode.

The beneficial effects of the invention are: the invention can reduce the uncertainty of manual operation, improve the automation control level of denitration system equipment, and reasonably cooperate with related equipment to meet the requirements of environmental protection, reduce the ammonia injection amount, reduce the production and operation cost and create certain economic benefits for enterprises.

Description of the drawings

FIG. 1 is a control diagram of a denitration system of a 350MW unit of a certain plant.

Fig. 2 is a diagram of an arrangement of on-site manual gates for 660MW units of a plant, equipped with 6 SCR units with manual gates.

FIG. 3 is a diagram showing the manual opening distribution of ammonia injection after the 660MW unit of a certain plant implements the present invention, and the length of the arrow indicates the amount of ammonia injection.

The concrete implementation mode is as follows:

the concrete implementation method of the patent technology of the invention is as follows, under the condition that the unit load is certain and the ammonia spraying amount is certain, the middle part of the unit has larger influence as an example:

1. the 6 manual gates controlling the ammonia injection amount were first fully opened to a maximum.

2. The manual valves #3 and #4 in the middle are closed by about 20% when being fully opened, and whether the opening degrees of the two valves are changed or not is determined according to the signal change condition of the denitration outlet.

3. And (3) closing the manual doors #2 and #5 by about 10% under the condition of full opening, and determining whether to change the opening degrees of the two valves according to the signal change conditions of the denitration outlet, the desulfuration inlet and the clean flue gas.

4. And (3) closing the #1 and #6 manual valves by about 5% from the condition of full opening, and determining whether to change the opening degrees of the two valves according to the signal change conditions of the denitration outlet, the desulfuration inlet and the clean flue gas.

Through the adjustment of the steps, the clean flue gas Nox signal of the denitration system is smaller than the flue gas Nox signal of the desulfuration inlet by about 10mg/Nm3, and the flue gas Nox signal of the desulfuration inlet is smaller than the NOx signal of the denitration outlet by about 10mg/Nm3, so that the problem of signal hang-over is solved

Similarly, the denitration system designed into 8, 12 or 16 manual doors can be adjusted according to the adjustment control mode, the control effect is relatively better, the problem that denitration signals are hung upside down can be basically solved through the adjustment control mode, when the unit load changes, clean smoke cannot exceed the standard for a long time, and the clean smoke can be quickly reduced under the automatic control condition even if the clean smoke exceeds the standard for a short time.

Claims

1. A control method for solving the problem of the inverted suspension of Nox signals of a coal-fired boiler in a thermal power plant is characterized by comprising the following steps: the diluted ammonia gas is reasonably distributed to each nozzle through manual door control adjustment, the nozzles with large influence on NOx signals of a denitration outlet adopt a less-spraying control mode, so that the NOx signals of the denitration outlet are controlled to be larger than those of the desulfurization inlet flue gas, and the NOx signals of the desulfurization inlet are controlled to be larger than those of clean flue gas.