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A new breakthrough in the design of cold box piping - air separation and filtration equipment
2017-02-17897
The pipes in the cold box of air separation and filtration equipment are all installed at normal temperature and operated at low temperature. The materials of the selected pipes and pipe fittings are basically low temperature resistant aluminum alloy and austenitic stainless steel. Different from the ordinary process pipeline, any problem in the design, stress analysis and installation inspection of the pipeline in the air separation cold box may cause serious deformation and crack of the pipeline in the cold box, cause medium leakage, and even damage the container equipment, leading to the major accident of cold box sand removal.
In addition to some problems encountered in the design process of ordinary air separation and filtration equipment, the impact factors such as pipeline rigidity, flexibility, pipeline support strength and operation under variable conditions should also be considered in the cold box pipeline design of 100000 m3 / h air separation and filtration equipment of Shenhua Ningxia coal
I. pipeline design
Six schemes have been designed in the early stage for the layout of equipment and pipes in the cold box of 100000 m3 / h air separation and filtration equipment of shenhuaning coal.
Scheme 1: lower tower and main cooling combination (middle empty barrel section), upper tower landing, beside the efficiency tower;
Scheme II: combination of lower tower and main cooling (no empty barrel section in the middle), landing of upper tower, beside the efficiency tower;
Scheme 3: lower tower, main cooling tower and synergist tower combination (middle empty barrel section), upper tower landing;
Scheme IV: combination of lower tower, main cooling tower and synergist tower (no empty barrel section in the middle), and landing of upper tower;
Scheme 5: optimize the size of cold box on the basis of scheme 3;
Scheme 6: optimize the size of cold box on the basis of scheme 4.
1.1 equipment layout
Through the design comparison of six schemes, considering the design and manufacturing process, transportation conditions, overall layout height, process technological realization, cost and actual land occupation of the user's site and other factors, scheme I is finally selected as the final implementation scheme. Combined with the general drawing and flow chart, the equipment layout is continuously optimized and refined in the process of modeling design. The final equipment layout is as follows: the lower tower in the main cooling box and the main cooling combination (the middle filling empty barrel section), the upper tower landing, and the efficiency tower standing by the side of the half air; 6 plate fin heat exchangers (divided into 2 rows, 3 in 1 row) are arranged in front of and behind the plate cooling box, and 2 subcoolers are arranged in the middle; 3 high-pressure liquid oxygen pumps and 1 high-pressure liquid oxygen pump are arranged on the left side of the cooling box One high-pressure liquid nitrogen pump and two circulating liquid oxygen pumps are arranged behind the cold box, and the argon reserved compartment is arranged behind the main cold box
1.2 pipeline layout
PDMS software aided design is adopted for the cold box pipeline of 100000 m3 / h air separation and filtration equipment of Shenhua Ningxia coal. The pipeline layout is closely combined with the setting of pipeline supports and hangers. The vessels, vessel supports and cold box section steel are used to support the pipeline to the maximum extent. Some pipeline supports and hangers are combined to save the materials and space of supports and hangers and avoid the influence of the setting of pipeline supports and hangers on the normal safety of the pipeline Install. The pipes in and out of the tower are basically arranged along the tower by using the principle of synchronous shrinkage, and the pipe supports and hangers are set along the tower. The advantages of the arrangement are: (1) the size of the cold box can be optimized while improving the safety of the pipeline operation. (2) compared with the traditional layout of pipes along the wall of cold box, the materials of pipes, pipe fittings and pipe supports used in the design are significantly reduced and the economy is significantly improved. (3) due to the reduction of pipe fittings used, the resistance is correspondingly reduced, and the operation energy consumption is reduced. The installation position of the valve shall be adjusted continuously during the design process of the pipeline in the cold box to ensure the smooth pipeline.
Through the above coordination, many pipelines avoid detour, significantly reduce resistance, and contribute a lot to cost and energy consumption control. The main cooling and upper tower safety valves are designed to be ejected from the cold box, and the pipeline has no elbow and other resistance parts, so as to reduce the relief resistance of the safety valve. The pipeline behind the liquid expander and the pipeline behind the high-pressure throttle valve are converged, and the pipeline behind the liquid expander is taken as the main flow. Through this design, the pipeline resistance is reduced, so as to reduce the operation energy consumption of air separation equipment. The pipeline behind the high-pressure throttle valve is designed with a long enough straight buffer section to reduce pipeline vibration and ensure the smooth convergence of two streams of fluid. In order to minimize the influence of the pipe on the verticality of the tower and the pipe support on the uneven stress of the equipment, the large pipes should be arranged as evenly as possible in the circumferential direction along the tower. For example, two dn1300 mm pipes from the waste nitrogen to the upper tower are designed as the current bypass mode, which is to achieve this purpose.
Fluent software is used to analyze the flow field of pipes, and the influence of pipes and pipe fittings on the deflected flow is studied. Aft software is used to calculate the resistance of these pipes, and the influence of pipe fittings on energy consumption is studied. For example, the results of the analysis of the waste nitrogen out of the upper tower and the waste nitrogen out of the subcooler pipeline show that the consistency deviation of the equipment body plays a leading role in the influence of the bias flow, and the influence of the pipeline is very small. But from the perspective of reducing energy consumption, the pipeline will play a greater role.
According to the analysis results of fluent and aft software, the pipeline from the waste nitrogen to the subcooler is designed as 4-strand symmetrical arrangement, which can reduce the resistance and improve the space utilization rate of the plate cooling box. Place the main cold full measuring valve at the highest point of the pipeline to avoid hydrocarbon accumulation at the valve, so as to improve the process safety, and design reasonable compensation, cold insulation measures and protection brackets for the pipeline to ensure the operation safety of the pipeline. The inlet and outlet return lines of the liquid pump, the return lines of the high-pressure liquid pump and the outlet lines of the circulating liquid oxygen pump are all designed with a certain upward slope to ensure the smooth operation of the liquid pump. The size of the liquid pump compartment limits the layout of the pipeline. In order to ensure that the load of the pipeline on the pump is within the allowable range, the outlet pipeline of the high-pressure liquid pump
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