CN203311267U - Accurate control system for adding low-content oxygen to water supply - Google Patents

Abstract

Provided is an accurate control system for adding low-content oxygen to a water supply. A pipeline is arranged between a water condensing and supplementing tank and a downcomer at the outlet of a deaerator. A gate valve, a desalted water pump, a first stop valve, a second stop valve, a flow meter, a third stop valve, a desalted water flow control valve, a check valve and a fourth stop valve are arranged on the pipeline in sequence. The desalted water flow control valve and the flow meter are connected with a PLC control cabinet. The control method of the control system comprises the steps that: oxygen-enriched desalted water is added to the downcomer at the outlet of the deaerator; by means of water supply flow signals, the addition amount of the desalted water is controlled in the range from 1/1000 to 2/1000 of the flow of the water supply; by means of water supply dissolved oxygen signals and saturated vapor dissolved oxygen signals, the dissolved oxygen content of the water supply at an inlet of a coal economizer is controlled in the range from 5 to 15 Mu g/L, and the dissolved oxygen content of saturated vapor at the inlet of the coal economizer is controlled less than 3 Mu g/kg. The control system and control method provided by the utility model ensure that superheated steam and reheated steam is oxygen-free. A high-pressure water supply system is prevented against flow accelerated corrosion (FAC); and the accidents, which are caused by oxide skin of a steam flow system peeling off when the water supply is added with high-density oxygen, are avoided.

Description

A Precise Control System for Adding Oxygen with Low Feed Water Content

technical field

The utility model relates to the technical field of water chemical working condition control in thermal power plants, in particular to a precise control system for adding oxygen with low content of feed water.

Background technique

The existing feed water oxygenation treatment technology is to add oxygen to the downcomer at the outlet of the deaerator, and control the dissolved oxygen in the feed water at the inlet of the economizer to be 30-150 μg/L. Fluctuation, although various manufacturers have also carried out a lot of research work on reducing the fluctuation range of oxygen content, but the fluctuation range with the smallest fluctuation range is above 50μg/L. The root cause of the large fluctuations in the oxygen content of the feed water is the high compressibility of the gas, and the pressure at the adding point changes with the load of the unit. The control system adjusts the opening of the solenoid valve by feeding back the dissolved oxygen signal of the feed water to assist the feed water flow signal. Since the gas flow is very small, only a few liters per hour, for a 300MW unit, every change of 1L/h in the oxygen flow will cause the feed water Dissolved oxygen changes by more than 15μg/L, therefore, it is impossible to achieve precise control of feed water oxygen content in a small range.

Due to the high oxygen content of the feed water with the existing feed water oxygenation technology, there is generally more than 30 μg/kg of dissolved oxygen in the steam, which will cause the superheater and reheater scale growth of some units to accelerate, and eventually lead to The over-temperature pipe burst accident caused by shedding and blockage. Therefore, many units currently adopt AVT(O) weak oxidative feed water treatment technology, that is, do not add oxygen to the feed water, but rely on the residual trace oxygen at the outlet of the deaerator to maintain a weak oxidative working condition, and generally require the feed water to dissolve Oxygen is less than 10μg/L, but because the deaerator has a good deoxygenation ability, the dissolved oxygen content of the feed water at the outlet of the deaerator is generally below 2 μg/L, and the dissolved oxygen content of the feed water at the inlet of the economizer is basically 0 μg/L, that is to say , the dissolved oxygen in the feed water has been consumed, and the oxygen content is too small to meet the oxygen required to repair the damage of the passivation film. Therefore, the inhibitory effect on the FAC of the high-pressure water supply system is weak. In order to have sufficient oxygen content in the feed water, a small amount of oxygen needs to be added to the feed water. However, the oxygen content should not be too rich, otherwise there will be more dissolved oxygen in the superheated steam, which will affect the scale of the superheater and reheater of some units. Therefore, there is a need for an oxygenation technology that can meet the precise control of low-level dissolved oxygen.

Contents of the invention

In order to solve the above-mentioned problems in the prior art, the purpose of this utility model is to provide a precise control system for adding oxygen with low content of feed water, to ensure that the dissolved oxygen content of saturated steam is less than 3 μg/kg, and to ensure that superheated steam and reheated steam do not contain oxygen. It can not only prevent the occurrence of FAC in the high-pressure water supply system, but also effectively prevent the superheater tube burst accident caused by the growth and peeling of the scale in the steam flow system after adding oxygen to the water supply.

In order to achieve the above object, the utility model adopts the following technical solutions:

A precise control system for oxygenation with low feed water content, a pipeline is connected between the condensate makeup water tank of the power plant and the outlet drop pipe of the deaerator, and a gate valve 1, a desalinated water pump 7, a first stop valve 2, The second stop valve 3, the flow meter 10, the third stop valve 4, the desalted water flow regulating valve 9, the check valve 5 and the fourth stop valve 6, and the desalted water flow regulating valve 9 and the flow meter 10 are connected with a PLC control cabinet 8.

The control method of the above control system is: add oxygen-rich desalted water to the downcomer at the outlet of the deaerator in the water vapor system of the power plant, and the PLC control cabinet 8 controls the addition of desalted water to 1/1000-1/1000 of the feed water flow through the feed water flow signal 2/1000, the dissolved oxygen content in the feed water at the inlet of the economizer is controlled at 5-15 μg/L and the dissolved oxygen content of the saturated steam is less than 3 μg/kg through the dissolved oxygen signal of the feed water and the dissolved oxygen signal of the saturated steam.

Compared with the prior art, the utility model has the following advantages:

1. The utility model controls the addition of desalinated water through the feedwater flow signal, precisely controls the addition of oxygen to the feedwater, and can accurately control the oxygen content of the feedwater below 15μg/L, ensuring that the superheated steam and reheated steam do not contain oxygen. Therefore, it can not only prevent FAC in the high-pressure water supply system, but also effectively avoid accidents caused by scale peeling in the steam circulation system after adding high-concentration oxygen to the water supply;

2. The investment in equipment is small. At present, the price of a set of gas automatic oxygenation device is generally more than 300,000 yuan, and it needs to occupy a space of about 20m ² ; with this technology, only 2 sets (1 for use and 1 for standby) need to be added with a flow rate of no more than 10t /h (the specific rated flow rate is determined according to the size of the unit), desalinated water pump, 100m~200m stainless steel pipeline, 1 gate valve, 1 check valve, 4 stop valves, 1 flow meter, 1 flow regulating valve, 1 PLC control cabinet, the cost is about 150,000 yuan;

3. There is no dosing cost. When the unit is in normal operation, demineralized water should be replenished into the boiler. The position is to supplement the hot water well of the condenser. The utility model only directly supplements a small part of demineralized water into the outlet of the deaerator to drop Tube, therefore, dosing costs do not occur. At present, the international general feed water oxygenation treatment technology is to add oxygen to the downcomer at the outlet of the deaerator. Generally, the oxygen in steel cylinders (40L) is purchased. The annual oxygen consumption of a 600MW unit is about 400 bottles, and the cost is about 50,000 yuan;

4. There is no operation and maintenance cost. When oxygen is added, operators need to regularly check the pressure of the oxygen cylinder and replace the oxygen cylinder, and corresponding labor costs will be incurred. The utility model does not generate labor costs during operation;

5. There is no safety problem. There is a safety factor in the high-pressure oxygen cylinder, but after using desalted water, there is no safety problem in this respect.

Description of drawings

The accompanying drawing is a structural schematic diagram of the control system of the utility model.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment, the utility model is described in further detail.

As shown in the accompanying drawings, the utility model is a precise control system for adding oxygen with low content of feed water. There is a pipeline connected between the condensate water tank of the power plant and the outlet drop pipe of the deaerator, and the gate valve 1, desalination Water pump 7, first stop valve 2, second stop valve 3, flow meter 10, third stop valve 4, desalted water flow regulating valve 9, check valve 5, fourth stop valve 6, and desalted water flow regulating valve 9 A PLC control cabinet 8 is connected with the flow meter 10 .

When the unit is running normally and ready to add oxygen to the water, open the gate valve 1, the first stop valve 2, the second stop valve 3, the third stop valve 4, the check valve 5 and the fourth stop valve 6, and start the desalinated water pump 7, The PLC control cabinet 8 automatically adjusts the desalted water flow regulating valve 9 according to the feed water flow signal, so that the desalted water flow displayed by the flow meter 10 is 1/1000-2/1000 of the feed water flow, and according to the feed water dissolved oxygen signal and saturated steam dissolved oxygen signal , and further adjust the desalinated water flow rate by adjusting the desalinated water flow regulating valve 9, so that the dissolved oxygen content of the feed water is maintained within the range of 5-15 μg/L, and ensure that the dissolved oxygen content of the saturated steam is less than 3 μg/kg. When the unit is out of service or does not need to add oxygen due to other reasons, it is only necessary to stop the desalinated water pump 7, and close the gate valve 1, the first stop valve 2, the second stop valve 3, the third stop valve 4, the check valve 5 and the The fourth cut-off valve 6 is sufficient.

Claims (1)

1. A precise control system for oxygenation with low feed water content, characterized in that: a pipeline is connected between the condensate water tank of the power plant and the outlet drop pipe of the deaerator, and a gate valve (1) and a desalinated water pump are sequentially arranged on the pipeline (7), the first stop valve (2), the second stop valve (3), the flow meter (10), the third stop valve (4), the desalted water flow regulating valve (9), the check valve (5) and The fourth cut-off valve (6) is connected with the desalted water flow regulating valve (9) and the flow meter (10) with a PLC control cabinet (8).

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