Energy consumption and energy saving analysis of natural gas technology CNG compressors During the shrinking process of Zhu Xiaohua (China Petroleum Southwest Oil and Gas Field Company Sales Branch), the cooling effect of CNG compressors is directly related to the control of interstage temperature, and the interstage temperature to compressor Efficiency has a greater impact. For this reason, the relationship between temperature and energy consumption between stages and the relationship between optimal compression ratio and cooling conditions of multi-stage compression are analyzed. It is concluded that the improvement of cooling conditions can reduce energy consumption and can determine multi-level under given cooling conditions. The conclusion of compressing the optimal compression ratio.
The optimum compression ratio of CNG compressor energy-class temperature cooling is the clean and environmentally friendly energy source of Xinjin Station. The use of CNG as a clean and environmentally friendly energy source will bring good economic and social benefits. However, due to the late start of China's CNG technology, the process flow of CNG gas station is unreasonable and the overall performance of CNG compressor is not good enough, resulting in high energy consumption and low efficiency of the system operation, increasing the operating cost of CNG gas station, seriously restricting The development of the CNG industry. In order to improve the technical level and comprehensive benefits of CNG filling stations, it is necessary to systematically analyze the energy consumption of the operation to study and formulate improvement measures for energy saving and consumption reduction. As the core component of CNG compressor, the energy consumption is the main influencing factor of the energy consumption of the gas station. Therefore, it is of practical significance to study the energy consumption process and propose energy saving measures.
Through the investigation of the CNG filling station affiliated to the Southwest Oil and Gas Field Branch and the CNG filling station in Suining and Nanchong, the author found that the existing CNG filling station has large power, long running time, high power consumption and cooling water. The large amount and the original design defects in the modular design and construction make the important links such as compressor unit, system process configuration, parameter monitoring and automatic adjustment unreasonable, resulting in high energy consumption and low efficiency of the system, which brings CNG production and operation. A huge pressure.
Take the four CNG filling stations (Xinjin Station, Leshan Station 1, Leshan Station 2, and Ya'an Station) to which the company belongs. For example, the Sichuan Energy Conservation Technical Service Center will be the four in July 2006 and May 2007 respectively. The compressor unit of the gas station has carried out energy-saving monitoring and re-testing. The test results are as shown, indicating that the unit efficiency is low.
Unit efficiency 60.00% Leshan 1 station Leshan 2 station Ya'an station A unit Ya'an station B unit name CNG filling station investigation situation Pre-processed natural gas through the station filtration, metering, pressure regulation, into the natural gas deep dehydration with a certain pressure The device makes the natural gas water dew point reach the standard (GB18047-2000 vehicle compressed natural gas), and then enters the natural gas compressor through the washing tank to carry out multi-stage compression to make the pressure reach 25MPa, and enters the high, medium and low pressure through the priority control panel. The three sets of gas cylinders are temporarily stored, and then the natural gas vehicles are inflated by a priority control panel, a gas dispenser (or a direct gas supply from the compressor). When the gas volume in the gas cylinder is lower than the starting set point of the compressor, the compressor is restarted and the above process is repeated.
The theoretical cycle of the CNG compression process includes the following three assumptions: 1 the cylinder has no clearance and the seal is good, and the gas valve is switched in time; 2 the gas is in the state of inhaling and exhausting, that is, the state of inhalation is the same as that before the gas is sucked. State, the state when exhausting is the same as the state at the end of compression; 3 when the gas is compressed, it is performed according to the constant compression process index value.
Address: (610017) The theoretical cycle of the reciprocating compressor of Yusha Road, Chengdu City, Sichuan Province is as shown: The theoretical cycle of the theoretical cycle compressor of CNG compressor includes three forms: isothermal cycle, adiabatic cycle and multivariable cycle.
The so-called isothermal cycle means that the temperature of the gas remains constant during the compression process, and the equation PV of the compression process curve AB is constant. For the isothermal compression process, the cycle work consumed by 1 kg of ideal gas is represented by ABCDA.
During the compression of the adiabatic cycle, the gas does not exchange heat with the outside world. The equation of the gas adiabatic compression process curve is divided into ideal gas and actual gas. For ideal gases: constant, k is the gas adiabatic index; for actual gas: constant, k,. It is the volume insulation index.
The CNG compression theory cycle is a variable cycle. The so-called multi-variable cycle means that the compressed gas has heat exchange with the outside world. In the medium-variable compression curve, the AB' equation PF' is constant, and n is the variable process compression index, which can be regarded as 1 in the compressor. 3. Optimization of energy consumption parameters of CNG compressor 1. Relationship between compression temperature and efficiency of stage CNG compression theory cycle is a multi-variable cycle. The end temperature of the interstage compression process is calculated as follows: the pressure at the end point, Pa; T, is the starting point of gas compression. The choice of temperature n at the end point will affect the actual exhaust temperature of the compressor and the deviation of the calculated exhaust gas temperature, as well as the deviation of the actual power consumed from the calculated power. The cycle power of compressing 1 kg of ideal gas is: multi-variable compression 1kg actual The cycle of gas is: in order to obtain a formula. When the cylinder pressure indication map and the machine speed are known, the indicated power is expressed as: the cylinder should be the sum of the working volumes of the cylinders on both sides, m3; n is the process index, the low pressure stage is n=(0.95~0.99)k, and the high pressure stage is preferable. n=k; Lu', P2' are the average actual suction and exhaust pressure, Pa; actual compression ratio, from the above derivation, it can be concluded that the adiabatic cycle consumes the most power, the isothermal cycle consumes the least, and the variable cycle is between Between the people. The isothermal over-gas technology/57 process does not actually exist, but comparing it with the actual compression process can determine the economics of the actual process. If the intake air temperature of any stage is increased due to insufficient cooling, the power consumption of the stage will increase. The second stage intake air temperature will increase by 3 for each first stage intake air temperature. The power consumption of the stage is increased by about 1%. Therefore, in order to reduce the power consumption, the intake air temperature of the stage should be lowered, that is, the cooling effect before the stage is improved. The existing CNG compressor is multi-stage cooling, the cooling medium is water, and a tube-and-tube cooler is used. Taking a CNG filling station as an example, the inter-stage population and outlet temperature are shown in Table 1. The inter-stage and population temperature changes at various levels are large, indicating that the working effect of the interstage heat exchanger of the compressor needs to be adjusted and changed to improve the operating efficiency. Through the above analysis, it is known that the interstage temperature has a great influence on the compressor efficiency, and the interstage temperature control is directly related to the compressor cooling effect. Table 1 Compressed inlet and outlet temperature gauges of a CNG filling station compressor (T i Stage compression population temperature outlet temperature off, but to improve interstage cooling should pay attention to: improve cooling should not increase the resistance of the cooler, otherwise it may not be worth the loss. Cooling is reflected in the latter level of income, the resistance is reflected in the loss of the previous level. If the benefit of the latter stage is greater than the loss of the previous stage, the power consumption of the machine is reduced. If the loss of the previous stage is greater than the gain of the latter stage, the power consumption will increase. For on-site compressors, if the cooling water temperature is reduced or the water consumption is increased during operation, the intermediate cooling effect can be improved, but this will cause the interstage pressure to change, which has a complicated impact on the interstage power consumption. If a two-stage compressor is improved during operation, if the interstage cooling is improved, the interstage pressure is reduced, whereby the first stage pressure reduces power consumption, and the second stage pressure increases power consumption. Under normal circumstances, the increase in pressure-changing power consumption is less than the reduction in cooling and power consumption, so the energy consumption of the unit will still be reduced. 2. Multi-stage compression The optimal compression ratio temperature has a great influence on the compression ratio of a certain type of piston compressor. At present, the optimal compression ratio of multi-stage compression is optimized according to the effect of the intercooler (ie, cooling to the first stage). The suction temperature is determined irrespective of the pressure loss existing during the intermediate cooling, and the theoretical power consumption of the compressor is determined to be the minimum value, that is, when the pressure ratios of the stages are equal, the pressure ratio is optimally distributed. However, this is not the case. Since the actual intermediate cooling effect is not perfect and there is a certain pressure loss, the following discussion will discuss how to determine the optimal pressure ratio based on the theoretical minimum power consumption of the compressor. In the 3-stage compression process, assuming that the multi-variable indices of each level are equal and n, the parameters of the first, second, and third levels are obtained; e is the total pressure ratio; and e is the pressure of the first, second, and third levels, respectively. Ratio; the relative pressure loss between the stages, that is, the ratio of the next stage suction pressure to the upper stage exhaust pressure, which is the ratio of the second stage suction pressure to the first stage discharge pressure, and the heart is the third stage intake. The ratio of pressure to the second-stage exhaust pressure; R is the gas constant; I, T, 2 are the intermediate cooling medium flow, the outflow temperature, K; E is the heat capacity ratio, £= C, C, respectively compressed Constant pressure specific heat of gas and medium-cooling medium, l/(kgI; m gas, m cold is the mass flow rate of compressed gas and medium-cooling medium, respectively, kg/s; a is coefficient, =¥%, subscript 1, 2 denotes the parameters of the first and second grades respectively; B is the heat exchange rate of the intermediate cooling, which is equivalent to the unit effective temperature difference, and the heat taken away from the unit displacement; q is the intercooling medium consumed by the unit displacement quality. For the thermal equilibrium analysis of the intermediate cooling, it can be obtained that: (1) the intermediate cooling temperature is obtained under the condition of t2=t3 and constant, and the optimum compression ratio is determined by = and 1=the lowest power consumption ds! The relationship of ds2 is as follows: It can be seen that the 3-stage compression is opposite to the 2-stage compression. As T increases, the first stage should be less pressed, and the second and third stages should be multi-pressure. From, it will greatly reduce power consumption. The effect of temperature on energy consumption and the improvement of cooling conditions can reduce energy consumption and change the status quo of low efficiency. When the work is at a minimum, the pressure ratio of each stage of the compressor is distributed. Bu 1 due to Tf / U), so the value can be determined by iterative calculation method: In summary, under different cooling conditions, the optimal pressure ratio distribution of multi-stage compression is not the same, that is, the optimal pressure ratio distribution and cooling conditions related. The relationship between compression ratio and energy consumption is: with the increase of the variable compression index n, the optimal pressure ratio change of the first stage under different cooling conditions is not the same, and the deviation from the extreme point will cause an increase in power consumption; Decrease or decrease in T2 (B increase), regardless of enhanced interstage cooling (B increase)
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