Since the birth of the first domestically produced condensing hydrogen dryer in 1990, there have been more than ten manufacturers of hydrogen dryers nationwide. It mainly produces three types of hydrogen dryers: condensing hydrogen dryer, electronic refrigeration hydrogen dryer and regenerative adsorption hydrogen dryer. Some power plants have selected several products, but the hydrogen humidity in the generator has not reached the standard. In some power plants, after the hydrogen dryer is installed, the hydrogen humidity in the generator has reached the standard, but frequent failures and major repairs and maintenance The amount is a headache. In view of the above, many power plants are at a loss as to how to choose a suitable hydrogen drying equipment, so they set their sights on expensive foreign similar products. So what type of hydrogen dryer can be really suitable for the current use in power plants in China? Next, I will make an introduction on this topic combined with the technology and experience accumulated by our company in the development, production and installation of adjustable hydrogen dryers for more than ten years.
Let's first analyze the dehumidification requirements of hydrogen in the generator.
According to DL / T651-1998 "Technical Requirements for Hydrogen Humidity of Hydrogen-Cooled Generators", the hydrogen dew point of generators operating at ambient temperatures above 20 ° C is not greater than 0 ° C and not less than -25 ° C, operating at ambient temperatures 0-20 The hydrogen dew point in the generator at ℃ is not greater than -5 ℃ and not less than -25 ℃. Since the hydrogen drying cycle of the generator is only a part of the cycle, in order to meet the hydrogen humidity requirements of the generator, the optimal range of the dew point under the working pressure of the hydrogen at the outlet of the hydrogen dryer is -15 ℃ —-25 ℃.
The sources of moisture in the generator are mainly the moisture in the sealing oil, the moisture in the hydrogen from the hydrogen production station, the moisture generated by the combination with a small amount of oxygen present, and the moisture remaining inside the unit just after maintenance. At present, the water content of the seal oil of hydrogen-cooled generators in China is generally high. When the generator does not leak oil, a small amount of water in the seal oil penetrates through the seal bush and enters the hydrogen in the generator, and the generator leaks oil In the case of a large amount of water directly evaporates into the hydrogen in the generator. At present, most of the generators in China have leakage of sealing oil into the machine. Overall, the source of moisture in hydrogen in generators is generally larger.
According to our experience, at present, all hydrogen dryers that can cause hydrogen leakage in all 200-600MW generators with severe oil leakage and high hydrogen humidity to reach the standard within 72 hours must meet the following conditions: The hydrogen dryer must be oil-resistant and able to Smooth oil discharge and sewage discharge; for the intermittent dehumidification hydrogen dryer, the hydrogen treatment capacity should be above 80Nm3 / h, and the continuous dehumidification time for the dew point of the outlet hydrogen working pressure below -15 ℃ should not be less than 2 hours. The intermittent time should not exceed 1 hour. For the continuous dehumidification hydrogen dryer, the hydrogen treatment capacity should be above 50Nm3 / h, and the dew point of the outlet hydrogen working pressure should be below -15 ℃. In order to ensure the hydrogen dehumidification applicable to all generators, the hydrogen dryer must meet the above conditions before it can be promoted and applied.
Let's analyze the dehumidification principles, advantages and disadvantages of several types of hydrogen dryers.
There are two methods for dehumidifying hydrogen. One is condensing dehumidification, that is, using refrigeration equipment to reduce the temperature of hydrogen, so that the moisture in it is precipitated in the form of condensation or frost, and then the defrosted water is discharged. , So as to achieve the purpose of hydrogen dehumidification. The other is adsorption dehumidification, that is, to make hydrogen flow in a container equipped with a hygroscopic agent, so that the moisture in it is absorbed by the hygroscopic agent, so as to achieve the purpose of dehumidifying the hydrogen. According to the different refrigeration equipment used, condensing dehumidifiers are divided into mechanical refrigeration and electronic refrigeration. The former is usually called a condensing hydrogen dryer; the latter is called an electronic refrigeration (or semiconductor refrigeration) dryer.
We know that mechanical refrigeration technology is currently a mature technology, which can achieve a large cooling capacity and a very low cooling temperature more economically, and has been widely used. Due to the advent of environmentally friendly refrigerants R134A, R404, R407, R410, etc., mechanical refrigeration no longer has to worry about environmental protection issues. Due to the use of mechanical refrigeration and metal heat exchanger structure, the condensing hydrogen dryer has low refrigeration temperature, high efficiency, easy control of cooling capacity and temperature, large dehumidification flow rate, good dehumidification effect, and is not affected by oil pollution and dust in hydrogen. Advantages, the hydrogen dehumidification system is independently closed, there is no easy leakage point and possible ignition point, and the safety is very good. Because the mechanical refrigeration equipment is a rotating pressure-bearing equipment, it has the problems of easy leakage and failure, and the maintenance is professional and difficult. This is a common problem with condensing hydrogen dryers. But these problems are not difficult to solve through the improvement of technology and the improvement of technology.
Electronic refrigeration is an artificial refrigeration technology developed in the 1950s. Its refrigeration method is: arrange a large number of P and N-type semiconductor materials in the same direction between two metal plates to form the same direction of different conductor contact surfaces , Made of refrigeration components. When a certain DC current is applied to the cooling component, the Peltier effect will occur on the contact surface of the dissimilar conductors, the temperature of one end (heat Rui) will release heat, and the temperature of the other end (Leng Rui) will decrease to absorb heat, thus achieving cooling the goal of. Because there is no rotating equipment for electronic cooling, the electronic cooling type hydrogen dryer has the advantages of no wear, vibration, noise, environmental pollution, and low maintenance. However, the electronic refrigeration technology is still not widely used so far, because there is no one kind of Peltier effect with strong conductor contact surface. At present, the Peltier effect of semiconductor refrigeration components is still weak, and the cooling efficiency is very low. At the same time, the contact surface of dissimilar conductors with Peltier effect is thin, the thermal conductivity of the material is large, and the heat conduction between the cold and hot surfaces is strong. Therefore, electronic cooling is not conducive to heat preservation. As the depth of refrigeration increases, the cold and hot surfaces Heat conduction is strengthened, and the refrigeration efficiency of electronic refrigeration will be further lowered (the energy cooling utilization rate of 30 ° C to -15 ° C is less than 10%, and the actual refrigeration coefficient is less than 0.4). It is not economical to use semiconductor refrigeration components for low temperature refrigeration. This refrigeration technology is currently only applicable to the cooling of micro-environments, and is not suitable for the hydrogen dehumidification of generators that require large cooling capacity. In addition, due to the current performance and quality constraints of semiconductor refrigeration components, the failure rate of electronic refrigeration dryers is also high.
The regenerative adsorption dryer has the advantages of low outlet hydrogen humidity, good dehumidification effect, low vibration and noise, and no failure. Due to the use of hygroscopic agent for dehumidification, the main disadvantage is that the amount of hydrogen treatment is small, and the oil dirt and dust in the hydrogen have a great influence on the dehumidification effect, and even make the hygroscopic agent lose its ability to remove moisture. Uniform changes, such as when heating, the moisture absorber particles heat first outside and then heat inside; when cooling, the desiccant particles cool first outside and then cool inside. Due to thermal expansion and contraction, internal stress changes occur. This change will eventually cause the powder of the absorbent to be powdered. The powder may be brought into the generator by the flow of hydrogen, causing pollution to the generator. Therefore, the absorbent must be cleaned or replaced regularly. The maintenance workload and work difficulty are relatively large. In order to overcome the adverse effects of oil pollution and powdering of the hygroscopic agent, a filter device must be installed to complicate the equipment and increase the amount of maintenance. If the generator has oil leakage, the dryer should be carefully selected. There are many valves and joints on the pipeline of the adsorption hydrogen dryer, so there may be many leakage points. There are fans and heaters in direct contact with the hydrogen. If the purity of the hydrogen is not high, combustion or explosion will occur. Therefore, the adsorption hydrogen drying The safety hazard of the device is very large, and it is necessary to check the leak and gas replacement before use.
Through the above analysis, we can see that the condensing hydrogen dryer can be applied to all hydrogen-cooled generators, and the regenerative adsorption dryer is suitable for generators with less oil leakage. Due to the limitations of electronic refrigeration technology, electronic refrigeration dryers are difficult to meet the dehumidification requirements of generators and should be eliminated as soon as possible.
At present, most of the generators in China have leakage of sealing oil into the machine. Therefore, only the condensing hydrogen dryer is suitable for widespread use in power plants in China. The regenerative adsorption dryer is more difficult to completely solve the oil pollution problem and the leakage problem, the cost is higher, and it must be regularly maintained, the operation cost is higher, and the hidden safety risks are very large, so it is not easy to promote the use.
Due to the shortcomings of condensing hydrogen dryers, which are relatively easy to leak, easy to malfunction, professional in maintenance, and difficult, the design, manufacture and selection of condensing hydrogen dryers should consider the following aspects.
1. Reasonable structure, smooth oil and sewage discharge, and the overall appearance is as small and beautiful as possible.
2. Adopt anti-vibration structure and anti-leakage measures, but keep the refrigeration system resistant to vibration and no leakage; adopt advanced refrigeration equipment and technology to eliminate the problem of easy leakage and failure of the condensing hydrogen dryer.
3. Considering the dismantling and repairing of the whole machine, it is very easy to install, dismantle, repair and replace the whole machine, and design simple and easy repair and maintenance processes, so that non-professionals can easily refer to the maintenance process manual. Carry out repairs and maintenance.
4. Intelligent automatic control system, the operation is as simple as possible, and can automatically analyze and indicate various faults or abnormal conditions. Follow the instructions and refer to the repair process instructions to easily repair and maintain. Simplify repair and maintenance work.
5. Precise temperature control operation, the refrigeration temperature is controlled to fluctuate between -15 ℃ -35 ℃, so that the compressor has sufficient rest time to extend its service life.
6. For the intermittent dehumidification hydrogen dryer, the hydrogen treatment capacity should be above 80Nm3 / h, the continuous dehumidification time of the refrigeration temperature below -15 ℃ should be no less than 2 hours, and the defrost intermittent time (including the refrigeration temperature is- Time above 15 ℃) should not exceed 1 hour. For the continuous dehumidification hydrogen dryer, the hydrogen treatment capacity should be above 50Nm3 / h, and the refrigeration dehumidification temperature should be below -15 ℃.
7. The operation is safe and reliable, and the whole machine should be designed for explosion-proof according to the requirements for the explosion-proof operation of the hydrogen system. Has the necessary explosion-proof performance.
8. Comply with environmental protection requirements and design according to green environmental protection requirements.