Development status and energy saving benefits of condensate recovery system

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Development status and energy-saving benefits of condensate recovery system 1 Overview Steam, as a heat energy carrier, is widely used in industrial fields such as power generation, petroleum, chemical industry, printing and dyeing, papermaking, textiles, brewing, rubber, ceramics, etc. After the steam releases the latent heat of vaporization in various steam-using equipment, it turns into saturated condensate water at nearly the same temperature and pressure. Since the operating pressure of steam is greater than the atmospheric pressure, the heat contained in the condensed water can reach 20%-30% of the total heat of the steam. The higher the pressure and temperature, the more heat the condensed water has, and the greater the proportion of the total heat of the steam. It can be seen that 100% recovery of heat from condensation water and effective utilization has great energy-saving potential. At present, in view of the increasingly significant economic and social benefits of condensate water recycling, as well as the problems caused by energy shortage, many companies have paid attention to the condensate produced in production, in order to save energy, protect the environment, and reduce production costs through effective waste heat utilization. Technical renovation projects for condensate water recycling are constantly being launched, but how to effectively process and utilize condensate water and how to achieve optimal economic benefits is a question worth studying. 2 Characteristics of the condensate recovery system Generally speaking, the condensate recovery system can be divided into two categories: open type and closed type [2]. 2.1 Open recovery system The open recovery system recovers condensate water into the water feed tank of the boiler. During the recovery and utilization process of condensate water, one end of the recovery pipeline is open to the atmosphere. Usually the condensate water collection tank is open to the atmosphere. When the pressure of the condensate is low and cannot reach the reuse site by self-pressure, a pump can be used to pressurize the condensate. The advantages of this system are simple equipment, easy operation and small initial investment. ； However, the economic benefits of the system are poor, and because the condensate water is in direct contact with the atmosphere, the dissolved oxygen concentration in the condensate water increases, which easily causes equipment corrosion. This system is suitable for small steam supply systems, systems with small amounts of condensate water and small amounts of secondary steam. When this system is adopted, the amount of steam should be minimized to reduce thermal pollution and loss of working fluid and energy. 2.2 Closed recovery system In a closed recovery system, the condensate water collection tank and all pipelines are under constant positive pressure, and the system is closed. Most of the energy contained in the condensate water in the system is directly recovered to the boiler through certain recovery equipment. The recovery temperature of the condensate water is only lost in the cooling part of the pipe network. Due to the sealing, the water quality is guaranteed, which reduces the cost of water treatment for recovery into the boiler. The advantage is that the economic benefits of condensate recovery are good and the equipment has a long working life. However, the initial investment of the system is large and the operation is inconvenient. Open and closed recovery systems are only general classifications of condensate recovery systems. Specific condensate recovery systems also have different recovery systems based on specific project conditions, such as on-site conditions of condensate, state parameters of condensate, recovery purposes, etc. 3 Determination of recovery methods and equipment For different condensate transformation projects, the selection of recovery methods and equipment is a crucial step in whether the project can achieve the investment purpose. First of all, to correctly select the condensate recovery system, it is necessary to accurately grasp the condensate volume and condensate drainage volume of the condensate recovery system. If the calculation of the condensate water volume is incorrect, the diameter of the condensate water pipe will be selected too large or too small. Secondly, it is necessary to correctly grasp the pressure and temperature of the condensate water. The pressure and temperature of the condensate water are the key to selecting the condensate water recovery system. The recovery system uses what method, what equipment to use, how to arrange the pipe network, whether it is necessary to use secondary steam, whether it is necessary to recover all the heat of the condensate water, and other issues are related to the pressure and temperature of the condensate water. Third, the selection of traps for the condensate recovery system is also something that the recovery system should pay attention to. Different types of traps will affect the pressure and temperature when the condensate is used, and will also affect the steam leakage of the recovery system. Due to the continuous improvement and improvement of the current condensate recovery technology, the continuous improvement of condensate recovery equipment and the continuous development of new high-performance recovery equipment, the condensate recovery system has the possibility of effectively utilizing various resources of condensate. * * improve. In the past, the recovery equipment used in the condensate recovery system was generally traps, water collection tanks, ordinary water pumps, etc. Problems existing in the recovery system, such as water hammer in the pipeline caused by the coexistence of steam and water, steam leakage caused by improper selection of traps, cavitation problems caused by ordinary water pump operation, the problem of ineffective utilization of condensate, etc., have been gradually solved with the research and development of recovery equipment. For example, in order to make full use of the steam content in the condensate water and effectively utilize its energy, a condensate water expansion tank is installed in the pipeline to flash the condensate water to generate secondary steam and recover the flash steam, thereby fully utilizing the energy and solving the water hammer problem in the pipeline. For another example, in order to solve the problem of cavitation in the pump of high-temperature saturated condensate, a high-temperature saturated condensate closed recovery device was developed based on the jet boosting principle [3] and based on advanced foreign technology. It also solves the cavitation problem in the injection boosting process of the jet pump, making it possible for the closed recovery system to make full use of the heat energy in the condensate water, recover the maximum amount of condensate water, save fuel and softened water, and improve the economy of the condensate water recovery system. Of course, there are other equipment, such as the JCRS-type heat pump-type condensate recovery device without traps developed using "heat pump" suction flash steam technology [4]. It uses a steam jet heat pump to boost the pressure of the flash steam of the condensate and recycle it to recover steam and water at the same time, so that the available steam volume is greater than the steam supply volume of the boiler. It can also reduce the temperature of the condensed water when the flash steam is sucked away, and then pump it back with an anti-cavitation pump for reuse, which has a significant energy-saving effect. In addition, a steam recovery compressor with a self-pressurizing ring pressurizing device can directly press steam and high-temperature condensate into the boiler at high temperature. This type of recovery equipment has a high heat recovery efficiency. The improvement of the condensate recovery device improves the recovery efficiency of the condensate recovery system. * * To improve, the selection of the device must not only consider the specific on-site conditions of the recovery system, but also the actual steam conditions such as steam pressure, temperature, flash steam recovery method, trap type, etc. When selecting a system, it is not that the higher the recovery efficiency of the system, the better. While the system achieves the purpose of recovery, the thermal economy of the system must also be considered. That is, while considering the waste heat utilization efficiency, the initial investment, that is, the economic and technical comparison of the project, can only be achieved through reasonable economic and technical comparisons to achieve a reasonable ratio of investment and recovery. This is the optimal solution for the project. Because closed recycling systems have higher efficiency and less environmental pollution, they are often given priority and adopted by recycling projects. 4. Thermal economic analysis of the condensate recovery project. For the closed condensate recovery system, the total investment is mainly the replacement or increase of the steam traps of the steam equipment. ； Recycling equipment - such as pumps, water collection tanks, heat exchangers, expansion vessels, high-performance recycling devices, etc., as well as insulation and pipe network materials, technical services, engineering construction costs, etc. The accumulation of several costs constitutes the entire project investment, and the investment situation needs to be determined based on site conditions and feasibility analysis of the project. The economic benefits of recycling projects are analyzed from the following aspects:: (1) Due to the use of a closed recovery system, the system operates in a closed manner, which increases the back pressure and reduces the amount of steam leakage, resulting in benefits ； (2) Recovery of condensate water saves the value of softened water ； (3) The increase in the condensate recovery temperature will increase the boiler inlet water temperature and save fuel consumption. Of course, there are also certain social benefits. Condensate water recovery can reduce pollution caused by the escape, evaporation, dripping and leakage of steam and condensate water, as well as wastewater discharge. Obviously, there is a certain relationship between the benefits and investment of the condensate recovery system. How to make the project reach a more optimized point in benefits and investment is a thermal economic issue that must be considered in the condensate recovery system. Usually, we use the investment payback period commonly used in engineering technology to determine the rationality and feasibility of project investment. After comprehensively considering the energy saving and economic issues of the condensate recovery project, the social and economic benefits of a recovery system are often significant. For example, a printing and dyeing factory uses the latent heat of vaporization released by steam to complete drying, cooking and other process requirements. After the steam is released, it is not recycled and is directly discharged to the ditch through a drain valve. The softened boiler feed water enters the deaerator when the temperature is very low, consuming a large amount of high-temperature steam and increasing the steam production of the boiler, thus consuming a large amount of fuel and causing high production costs. In order to reduce production costs, save water, and save energy, the factory adopts a closed condensate recovery scheme. The steam from the industrial dyeing vat is turned into condensate with a certain temperature and pressure through the trap, and enters the water collection tank. The flash steam generated in the water collection tank enters the boiler deaerator and can heat the feed water. ； The condensate water in the water collection tank is directly pumped into the deaerator through the anti-cavitation pump to recover the condensate water and its heat. A bypass is also provided to press the condensate water into the soft water tank and then enter the boiler. After adopting this project, the economic benefits obtained by the printing and dyeing factory are huge. If the benefits are calculated in units of one year, after the transformation, the plant will reduce the steam leakage of steam equipment by 864t/a. If the steam price is calculated at 70 yuan/t, it can bring annual benefits of 61,000 yuan to the plant. ； The benefit brought by saving softened water is 58,000 yuan/a ； Due to the increase in boiler inlet temperature and fuel saving, the benefit is 302,000 yuan/a. Its total annual income is 420,000 yuan/a. Considering that the equipment investment and various expenses totaled 350,000 yuan per year, through economic and technical comparison, the investment was recovered in less than ten months after the project was put into use. After the adoption of this system, the environmental pollution problems caused by leakage have been radically eliminated, and its social benefits are inestimable. 5 Conclusion As the world's energy becomes increasingly tense, energy conservation becomes more and more important. Condensate water recycling as an important energy conservation measure will receive more and more attention. And due to the widespread application of steam energy, the continuous improvement of condensate recovery technology and the research and development of condensate recovery equipment, the energy-saving benefits of condensate recovery will become more prominent.