The hottest new type of heat pump for paper machin

A new type of heat pump for paper machine drying

overview:

the paper industry is a high energy consuming industry. China's comprehensive energy consumption per ton of paper is 1.55-1.7t standard coal, 100 tons of water, and steam energy consumption accounts for 15% of the cost of paper making, far higher than the world's advanced level. Among them, paper drying is the main energy consuming process in papermaking process. The energy utilization rate of paper drying process is very low, and it also affects the output of paper machine and the quality of paper

in order to improve the energy utilization rate, the rational use of energy in the drying part of papermaking has attracted the attention of thermal energy workers, On the basis of introducing foreign advanced paper machines, the steam jet heat pump is gradually popularized in paper machine drying "In the application of cadres in neonatal nursing, the pressure difference between the fresh steam of the boiler and the steam of the dryer is used as the power to inject the flash steam of the return water of the dryer, which is reused after boosting the pressure. The use of steam jet heat pump reduces the back pressure of the condensate return water of the dryer, makes the return water unobstructed, reduces the accumulated water of the dryer, improves the speed of the dryer, and improves the output. On the other hand, the flash steam of the condensate is recovered, which reduces the amount of fresh steam of the boiler, so the heat pump condensate The water recovery device has been widely used in paper drying

the application effect of heat pump condensate recovery device is related to many factors, including the pressure difference between fresh steam and steam entering the dryer Δ P1, pressure difference between drying cylinder and flash tank Δ P2, and dryer grouping control mode, etc. These factors also affect the internal size of the heat pump, so the operation of the condensate flash steam recovery device for paper drying cadres has an important relationship with the performance of the heat pump. At present, the steam jet heat pump commonly used in the market is the volume regulating single nozzle heat pump. The specific structure is as follows:

it is composed of nozzle 1, mixing chamber 2 and diffuser section 3. When the output steam flow changes, it is adjusted by the driving steam regulating valve installed in front of the jet heat pump to maintain the outlet pressure unchanged. The regulating valve in front of the heat pump changes the steam flow through the nozzle by qualitative regulation, that is, the switch of the regulating valve changes the steam pressure behind the valve, the valve is turned down, and the pressure behind the valve is reduced. Although the flow area of the nozzle remains unchanged, the flow through the nozzle is reduced. Due to the throttling of the regulating valve, the steam work capacity is lost, so the ejection capacity of the driving steam is greatly reduced. The experiment shows that when the flow of the driving steam decreases by 20%, the ejection capacity of the driving steam decreases to zero [1]

Figure 1 shows the characteristic curves of various adjustment modes of heat pump. The ordinate is the flow GP of the driving steam, the abscissa is the outlet flow GC of the heat pump, and the OA line is the midpoint of the rectangular coordinate

Fig. 1 adjustment mode of jet heat pump

on line 0A gc=gp, that is, the heat pump does not inhale low-pressure steam. Suppose that the output flow of the heat pump is required to be gc=gcb, until after point a, G, which is abbreviated as C> GP by the American Society for testing and material, the flow through the nozzle G P will not increase, and the low-pressure steam flow GH will continue to increase. Line 0ab is the case that the heat pump has no means of regulation, and the change of flow is only controlled by the outlet valve of the heat pump. When the outlet flow GC is less than the flow of the nozzle, do not extract low-pressure steam. During the implementation of quality regulation, that is, when the regulating valve is installed on the inlet pipeline of the driving steam, the characteristic curve of the heat pump becomes 0cb, that is, at point C, the flow through the nozzle is less than the output flow, and the heat pump begins to suck in low-pressure steam. The driving steam flow GP at point C is about 70% of the design value. If quantity regulation is implemented, a needle regulating valve is installed in the nozzle to change the throat area of the nozzle, which is the minimum section of the supersonic nozzle, In this section, the steam flow velocity is the sound velocity, and the change of pressure behind the nozzle does not affect the flow velocity of the throat section. Therefore, changing the throat area can keep the outlet area of the heat pump unchanged. The steam pressure in front of the nozzle remains unchanged. At this time, the characteristic curve of the heat pump is 0dB, that is, at point D, the heat pump begins to suck in low-pressure steam, and the driving steam flow GP at this point is about 50% of the design value. Therefore, quantity regulation and quality regulation improve the effective operation range of heat pump. In order to improve the effective operation range of the heat pump, the patented multi nozzle volume regulating heat pump developed by Shenyang Feihongda energy saving equipment technology development Co., Ltd. can operate effectively when the output flow is from 30% to 100%, and its characteristic curve is shown in figure 0efghib

this curve represents the flow characteristics of the three nozzle jet heat pump. The first nozzle starts to suck in low-pressure steam from point E, the second nozzle starts to open at point F, and the third nozzle starts to open at point h until the design output flow is reached at point B. 744 ⑵ 006 "standard acupuncture experiment of nickel metal hydride batteries for electric vehicles" B is the characteristic line with the injection coefficient u=const, and operation according to 0b is the most efficient operation mode, It can be seen that 0efghib is very close to line 0b. The more nozzles there are, the closer the operation curve is to line 0b, and the higher the efficiency. At present, the commonly used heat pump control mode in paper machine drying is quality regulation. As shown in Figure 2

Figure 2 paper machine dryer heat pump control mode

in order to keep the output pressure of the heat pump unchanged, a pressure transmitter is installed at the outlet of the heat pump to control the opening of the bypass regulating valve 1, and at the same time, the opening of the regulating valve 2 is controlled by the difference between the outlet pressure of the heat pump and the flash steam pressure (differential pressure transmitter). In the above control mode, some steam enters the dryer through the bypass regulating valve, causing throttling loss and reducing the utilization rate of heat energy. By using quality regulation, the regulation range of single nozzle heat pump is small, and it is difficult to keep the pressure difference between the outlet steam and flash steam of the heat pump unchanged when the fresh steam pressure drops, the vehicle speed changes, and the steam consumption of the dryer changes. The volume regulating multi nozzle heat pump has a large effective working range, so there is no need to add a bypass regulating valve, which saves investment. Figure 3 shows the schematic diagram of the dual nozzle heat pump with conditional capacity regulation and contraction experiment. When working, open 1# first, and open 2# valves in sequence if the requirements cannot be met. According to the variation range of working conditions, the two nozzles can be made the same or different

Figure 3 Schematic diagram of dual nozzle heat pump with volume regulation

compared with single nozzle mass regulation heat pump, flash steam can be used more, and the energy saving effect is remarkable. The bypass regulating valve is reduced, and the total investment is reduced. The pressure in the flash tank is determined by the back pressure of the orifice drain valve. During the design, the diameter of the orifice drain hole is determined according to the pressure difference between the dryer and the flash tank and the return water volume

the double nozzle volume regulating jet heat pump has achieved satisfactory results in the trial of 2500 paperboard machine. (end)