TY - JOUR
AU - Najafi, Atabak
AB - Abstract In city gas pressure reducing stations, in order not to hydrate natural gas after a sudden drop in pressure, the gas temperature is raised by a heater. The increase in temperature is such that after the pressure drop, the gas inside the pipes does not freeze. These heaters are gas burning and very high consumption, and because they use fossil fuels, produce environmental pollution. Accordingly, in this research, solar energy will be used to preheat the gas, which will be used for the most accurate analysis of TRNSYS software. In this regard, the amount of utilization of the sun and the amount of energy required for preheating will be obtained. After the implementation of the TRNSYS program, the highest amount of energy supply by the sun is related to spring, which on this day provides 55% of the thermal energy required by the load by solar energy. 1. INTRODUCTION Gas supply, in order to better transfer the gas to the consumption points and to compensate for the pressure drop due to the long path, increases the gas pressure to a high extent. Considering that consumers need gas with different pressures according to their type of consumption; therefore, for this coordination and pressure regulation, pressure reduction stations have been installed in the route [1–3]. This station has equipment that reduces the gas pressure to the desired level. Because a sudden drop in pressure causes the temperature to drop; therefore, in the station, a heater is used to heat the gas before the pressure drops. The heater heats the operating fluid with a gas burner [4–7]. The gas that passes through the hot water through pipes absorbs heat and the temperature rises. This increase in temperature is such that it does not freeze after the pressure drop in the regulators. In these stations, to prevent high fuel consumption, renewable energy such as solar energy can be used [8–11]. The technology of using solar energy that produces thermal power is heat collectors. One of the collectors that produce high temperature with suitable flow is vacuum tube collector [12–15]. The operation of this gas station is such that the inlet gas with a pressure of ~1000 psi after filtration, its pressure must be reduced by regulators. This reduction in pressure causes an immediate decrease in the temperature of the gas, and since water vapor particles are always present in the gas; lowering the temperature causes hydration and, as a result, freezing of the gas inside the pipelines. To solve this problem, the gas temperature is raised before reaching the regulators. In [16], the authors conducted a research on a smart combination of a solar assisted absorption chiller and a power productive gas expansion unit for cogeneration of power and cooling. In the next study, authors conducted a research on performance analysis of using CuO-Methanol nanofluid in a hybrid system with concentrated air collector and vacuum tube heat pipe [17]. A research has been conducted on energy recovery through natural gas turbo expander and solar collectors: modeling and thermos economic optimization [18]. In [19], the authors conducted a research on energy and exergy analysis and multi-criteria optimization of an integrated city gate station with organic Rankine flash cycle and thermoelectric generator. In the next study, the authors conducted a research on thermodynamic modeling and analysis of a novel heat recovery system in a natural gas city gate station [20]. A research has been conducted on thermal modeling of indirect water heater in city gate station of natural gas to evaluate efficiency and fuel consumption [21]. Exhaust gas from refineries has a pressure of ~400–1000 psi, which reduces this pressure during the steps that reach the appropriate consumption pressure. In one of these steps (the first stage of pressure reduction in pressure reduction stations), pressure reduction also reduces the gas temperature. Because this gas contains some water vapor, a sharp drop in temperature can freeze the water molecules in the gas and thus block the gas supply path. For this reason, it is necessary to raise the temperature of the gas to such an extent that the pressure reaches a normal temperature after the pressure drops. This is done by a heat exchanger (heater) that is installed next to the station. This converter consists of a burner and a tank containing water (in the form of shells and tubes) that the gas absorbs the necessary temperature by passing by hot water. The fuel of this heat exchanger is gas and it is very high consumption. In addition, the gas caused by its combustion will have environmental consequences. Therefore, in order to optimize this system, both in terms of reducing fossil fuel consumption and in terms of reducing pollution, measures should be considered. In this research, solar energy has been used to raise the temperature of this gas. 2. METHODOLOGY Area of study In a research based on renewable energy sources, it is very important to determine the amount of resources because these resources are variable in relation to environmental factors and the existing information in the pool must be very carefully considered. Therefore, the intensity of solar radiation is determined as an average daily for a year. In this research, the study area with the geographical characteristics listed in Table 1, which is related to Hamadan, is considered below, and in Figure 1, the average of daily ambient temperature in Hamadan City can be seen. Gas station studied Geographical characteristics of the studied area (http://www.irimo.ir). Table 1 Geographical characteristics of the studied area (http://www.irimo.ir). Parameter . Quantity . Unit . Location Hamedan Latitude +35.44 ° Longitude +44.23 ° Altitude 1803 M Parameter . Quantity . Unit . Location Hamedan Latitude +35.44 ° Longitude +44.23 ° Altitude 1803 M Open in new tab Table 1 Geographical characteristics of the studied area (http://www.irimo.ir). Parameter . Quantity . Unit . Location Hamedan Latitude +35.44 ° Longitude +44.23 ° Altitude 1803 M Parameter . Quantity . Unit . Location Hamedan Latitude +35.44 ° Longitude +44.23 ° Altitude 1803 M Open in new tab Specifications of the studied gas heater. Table 2 Specifications of the studied gas heater. Parameters . Unit . Quantity . Heater capacity SCMH 5000 Inlet pressure(Pout) PSI 1000 Outlet pressure(Pin) PSI 1000 Inlet gas temperature(T G-in.h) °C 10 Exhaust gas temperature(T G-out.h) °C 50 Area of tube m2 7 Gas flow m3/hr 5000 Combustion efficiency 45% Parameters . Unit . Quantity . Heater capacity SCMH 5000 Inlet pressure(Pout) PSI 1000 Outlet pressure(Pin) PSI 1000 Inlet gas temperature(T G-in.h) °C 10 Exhaust gas temperature(T G-out.h) °C 50 Area of tube m2 7 Gas flow m3/hr 5000 Combustion efficiency 45% Open in new tab Table 2 Specifications of the studied gas heater. Parameters . Unit . Quantity . Heater capacity SCMH 5000 Inlet pressure(Pout) PSI 1000 Outlet pressure(Pin) PSI 1000 Inlet gas temperature(T G-in.h) °C 10 Exhaust gas temperature(T G-out.h) °C 50 Area of tube m2 7 Gas flow m3/hr 5000 Combustion efficiency 45% Parameters . Unit . Quantity . Heater capacity SCMH 5000 Inlet pressure(Pout) PSI 1000 Outlet pressure(Pin) PSI 1000 Inlet gas temperature(T G-in.h) °C 10 Exhaust gas temperature(T G-out.h) °C 50 Area of tube m2 7 Gas flow m3/hr 5000 Combustion efficiency 45% Open in new tab Figure 1 Open in new tabDownload slide Average of daily ambient temperature in Hamadan City of Iran (http://www.irimo.ir). Figure 1 Open in new tabDownload slide Average of daily ambient temperature in Hamadan City of Iran (http://www.irimo.ir). The station under study of this project is a station with a capacity of 5000 m3/hr, on which the equipment and facilities inside the station are also designed, so that the heater considered in this station should be able to heat gas with a flow rate of 5000 m2/hr to have the appropriate reliability. Table 2 shows the specifications of the heater according to IGS-M-PM-104 (2) standard. The temperature of the gas passing through the station in different stages of the station has different values. Figure 2 shows the temperature conditions of the gas passing through the station. Figure 2 Open in new tabDownload slide Different natural gas temperatures passing through a CGS station. Figure 2 Open in new tabDownload slide Different natural gas temperatures passing through a CGS station. Figure 3 Open in new tabDownload slide Gas station studied. Figure 3 Open in new tabDownload slide Gas station studied. One of the important parameters in suppression valves (regulators) is their temperature drop. This drop is calculated according to Figure 2 from the following equation: $$\begin{align} \varDelta{\mathrm{T}}_{\mathrm{v}}={\mathrm{T}}_{\mathrm{G}-\mathrm{Out}-\mathrm{h}}-{\mathrm{T}}_{\mathrm{G}-\mathrm{Out}-\mathrm{v}} \end{align}$$(1) Another important parameter is determining the hydrated temperature of natural gas passing through the station. In most stations, the gas temperature is increased unnecessarily for the sake of reliability, so that they can reduce the pressure to a great extent, without causing any damage to the technical equipment. It is now possible to calculate the exact temperature of the natural gas coming out of the heater, which is directly proportional to the fuel consumption of the heater. $$\begin{equation} {\mathrm{T}}_{\mathrm{G}-\mathrm{Out}-\mathrm{h}}={\mathrm{T}}_{\mathrm{hyd}}+\varDelta{\mathrm{T}}_{\mathrm{v}}+\varDelta{\mathrm{T}}_{\mathrm{safety}} \end{equation}$$(2) Another important parameter is determining the temperature of the inlet gas to the station. Given that the pipelines are buried at a depth of 1.5 m, it can be concluded that the temperature of the inlet gas is a function of ambient temperature and is obtained from the following equation. $$\begin{equation} {\mathrm{T}}_{\mathrm{in}}={\mathrm{T}}_{\mathrm{G}-\mathrm{in}-\mathrm{h}}=0.0084{{\mathrm{T}}_{\mathrm{atm}}}^2+0.31{\mathrm{T}}_{\mathrm{atm}}+11.403\end{equation}$$(3) Heat required for heating gas passing through the heater Based on the content expressed and according to the following relations, the required heat can now be calculated to heat the passing gas. $$\begin{equation} \textrm{Q} \ {_\mathrm{load}}={\mathrm{m}}_{\mathrm{G}}\times \varDelta \mathrm{h} \end{equation}$$(4) $$\begin{equation} \varDelta \mathrm{h}=\left({\mathrm{C}}_{\mathrm{p}2}\times{\mathrm{T}}_2\right)-\left({\mathrm{C}}_{\mathrm{p}1}\times{\mathrm{T}}_1\right) \end{equation}$$(5) According to the capacity of the station, the mass flow rate of the heater is considered in all calculations as 5000 m3/hr, and since ~85–95% of natural gas is methane, methane density can be used to convert gas flow rate from (m3)/hr to kg/s. The amount of passing gas in standard conditions is set at 0.853 kg/s. Also, the specific heat capacity of the gas entering the station, as mentioned, is calculated with the following equation due to its high percentage of methane at different temperatures. $$\begin{align} {\mathrm{C}}_{\mathrm{p}}&={\mathrm{C}}_0+{\mathrm{C}}_1\theta +{\mathrm{C}}_2{\theta}^2+{\mathrm{C}}_3{\theta}^3\kern0.50em \left(\mathrm{Kj}/\mathrm{Kg}\ \mathrm{K}\right)\nonumber\\ \theta& =\mathrm{T}\left(\mathrm{Kelvin}\right)/1000 \end{align}$$(6) Power of the heater The efficiency of heaters for gas heating is never 100%, so it must produce more heat than required. This heat is obtained by defining the combustion efficiency for the heater as well as the dissipation heat based on the following equation. $$\begin{equation} \textrm{Q}\ {_\mathrm{heater}}=(\textrm{Q} _{\ \mathrm{load}}/{\eta}_{\mathrm{combustion}})+\mathrm{Q}\ _{\mathrm{lost}} \end{equation}$$(7) Simulation of the gas station studied in TRNSYS In this project, TRNSYS software has been used to model and analyze the solar system (Figure 3). TRNSYS is a powerful software for analyzing transient solar cooling and heating systems. For the present system, a solar heating system using vacuum tube collectors with an area of 50 m2 and a constant speed circulator pump with a maximum flow rate of 1000 kg/hr and two shell tube converters and a heater with gas fuel have been used. Also, printers have been used to record the outputs as diagrams for different seasons. The weather conditions of Hamedan city are available in the software library. The design of the project is as follows. The slope of the collector has been adjusted considering that it should absorb the most energy from the sun during the year. To have the maximum solar fraction, pump discharge and to optimize the system, the number of pipes passing through the converters was extracted from the software according to the Table 3. Solar fraction Table 3 Specifications of the solar system. Collector angle . 200 . Pump discharge 1000(kg/hr) Pipes passing through converters 150 Collector angle . 200 . Pump discharge 1000(kg/hr) Pipes passing through converters 150 Open in new tab Table 3 Specifications of the solar system. Collector angle . 200 . Pump discharge 1000(kg/hr) Pipes passing through converters 150 Collector angle . 200 . Pump discharge 1000(kg/hr) Pipes passing through converters 150 Open in new tab The solar fraction is defined as the percentage of energy required to heat the gas. $$\begin{equation} \mathrm{SF}=\textrm{Q}\ {_\mathrm{sol}}/((\textrm{Q} _{\ \mathrm{sol}})+\textrm{Q}_{\ \mathrm{aux}}) \end{equation}$$(8) 3. RESULTS According to the diagrams obtained from the software, the solar fraction and the temperature of the collector output fluid are quite obvious. The recorded results of modeling for one day in different seasons of the year are presented in following Figures 4–11. Figure 4 Open in new tabDownload slide Average degree of fluid temperature on a summer day. Figure 4 Open in new tabDownload slide Average degree of fluid temperature on a summer day. Figure 5 Open in new tabDownload slide Average solar fraction corresponding to a summer day. Figure 5 Open in new tabDownload slide Average solar fraction corresponding to a summer day. Figure 6 Open in new tabDownload slide Average fluid temperature on a spring day. Figure 6 Open in new tabDownload slide Average fluid temperature on a spring day. Figure 7 Open in new tabDownload slide Solar fraction corresponding to a spring day. Figure 7 Open in new tabDownload slide Solar fraction corresponding to a spring day. Figure 8 Open in new tabDownload slide Fluid temperature on an autumn day. Figure 8 Open in new tabDownload slide Fluid temperature on an autumn day. Figure 9 Open in new tabDownload slide Solar fraction of an autumn day. Figure 9 Open in new tabDownload slide Solar fraction of an autumn day. Figure 10 Open in new tabDownload slide Fluid temperature on a winter day. Figure 10 Open in new tabDownload slide Fluid temperature on a winter day. Figure 11 Open in new tabDownload slide Solar fraction related to a winter day. Figure 11 Open in new tabDownload slide Solar fraction related to a winter day. According to Figure 4, the highest output temperature of the collector is related to 14:00 with a value of 153°C, for which the output temperature of Converter 2 is 115°C and the output temperature of Converter 1 is 96°C. For the summer, the amount of solar energy used to supply some of the heat required by the gas pressure reducing station can be seen in Figure 5. According to Figure 5, as can be seen, the highest amount of solar utilization is related to 14:00, in which the solar fraction is equal to 1; that means all the thermal energy needed to heat the fluid can be provided by solar energy. The average fluid temperature as well as the solar fraction for spring can be seen in Figures 6 and 7. According to Figure 6, the highest output temperature of the collector is related to 7:00 with a value of 89°C, for which the output temperature of Converter 2 is 70°C and the output temperature of Converter 1 is 59°C. For spring, the amount of solar energy used to supply some of the heat required by the gas pressure reducing station can be seen in Figure 7. According to Figure 7, as can be seen, the highest amount of solar utilization is related to 11:00, in which the solar fraction is equal to 55%. This means that 45% of the remaining energy must be supplied through the auxiliary system. The average fluid temperature as well as the solar fraction for autumn can be seen in Figures 8 and 9. According to Figure 8, the highest output temperature of the collector is related to 14:00 with a value of 83°C, for which the output temperature of Converter 2 is 68°C and the output temperature of Converter 1 is 58°C. For autumn, the amount of solar energy used to supply some of the heat required by the gas pressure reducing station can be seen in Figure 9. According to Figure 9, as can be seen, the highest amount of solar utilization is related to 13:00, in which the solar fraction is equal to 52%. This means that 48% of the remaining energy must be supplied through the auxiliary system. The average fluid temperature as well as the solar fraction for winter can be seen in Figures 10 and 11. According to Figure 10, the highest output temperature of the collector is related to 13:00 with a value of 23°C, for which the output temperature of Converter 2 is 22°C and the output temperature of Converter 1 is 21°C. For winter, the amount of solar energy used to supply some of the heat required by the gas pressure reducing station can be seen in Figure 11. According to Figure 11, as can be seen, the highest amount of solar utilization is related to 14:00, in which the solar fraction is equal to 37%. This means that 63% of the remaining energy must be supplied through the auxiliary system. 4. CONCLUSION Since Iran has a good geographical position in terms of using solar energy to provide heating; therefore, it is necessary to pay attention to this clean and available renewable energy, due to the lack of energy in the future and environmental problems. Research and work in the field of solar energy, due to the novelty and novelty in the past decade, both in terms of software and hardware, is a flexible issue and sometimes depends on empirical reasoning. The result of the work to provide the necessary thermal energy in the pressure reducing station using solar energy with 50 m2 of vacuum tube collector and 1000 kg/hr constant flow pump and two tube shell converters is presented. According to the relevant diagrams, what is seen in the solar fraction diagram, each season provides a significant portion of the energy needed to heat the gas at the station with the help of the sun. 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TI - Energy analysis of vacuum tube collector system to supply the required heat gas pressure reduction station
JF - International Journal of Low-Carbon Technologies
DO - 10.1093/ijlct/ctab069
DA - 2021-10-07
UR - https://www.deepdyve.com/lp/oxford-university-press/energy-analysis-of-vacuum-tube-collector-system-to-supply-the-required-1506r4G5XF
SP - 1
EP - 1
VL - Advance Article
IS - 
DP - DeepDyve
ER -