1. Introduction of nano aerogel insulation felt
A long-distance oil pipeline in cold area is transporting crude oil with the temperature of - 10 ℃. because the ambient temperature in summer is obviously higher than the oil temperature, if the pipeline in the station is in direct contact with air, a layer of water film will condense on the wall surface, which is easy to cause pipeline corrosion, instrument failure and other phenomena, and seriously affects the safe operation of the pipeline in the station. because the pipeline needs to be insulated, the original pipeline insulation material is polyurethane foam insulation material, but this material has a series of shortcomings such as short service life, easy to damage and difficult to disassemble. in recent years, the newly developed nano aerogel insulation felt is a good solution to this problem
2. Comparison of heat preservation schemes of different heat preservation materials
According to the specific operation conditions of the pipeline and the temperature record data in summer in the area, the site conditions are set: 813 mm outside diameter, 16 mm wall thickness, oil temperature of - 10 ℃, ambient temperature of 35 ℃ ( the highest temperature in summer in the area for nearly two years ), the length of the pipeline is 1 m for calculation, and the wind speed of the outer wall of the pipeline is 2 m / S.. According to the common insulation materials of pipeline, three insulation schemes are given. scheme 1 uses 10 mm nano aerogel insulation felt to coat the pipeline. In scheme 2, 25 mm insulation rubber and plastic is adopted to coat the pipeline; In scheme 3, 17 mm polyurethane foam insulation material was used to coat the pipeline, and the thickness of 25 mm and 17 mm were recommended values of insulation rubber and polyurethane foam insulation material under the temperature difference. the three schemes were combined with bare pipe to form four working conditions, and the insulation performance was compared and analyzed. The analysis resulted in the following results:
Bare pipe simulation results: according to the field situation, the thermal conductivity of steel pipe is 44.5 w / ( m k ). According to the simulation results, when no thermal insulation measures are taken, the temperature outside the pipe wall is - 9.24 ℃ under the set site conditions, indicating that the steel pipe has no thermal insulation effect basically.
Simulation results of scheme 1: the thermal conductivity of nano aerogel insulation felt is 0. 016 w / ( m k ). the simulation results show that when scheme 1 is adopted, the outside temperature of pipeline is 30. 624 ℃, lower than the ambient temperature of 4. 376 ℃, and the insulation effect is good. The outside temperature of the pipeline is higher than the dew point temperature of the air, and condensation phenomenon does not occur.
Simulation results of scheme 2: the thermal conductivity of rubber and plastics is calculated as 0.035 w / ( m k ). the simulation results show that when scheme 2 is adopted, the temperature outside the pipeline is 30.803 ℃ and 4.197 ℃ lower than the ambient temperature under the set site conditions, and condensation will not occur at this temperature.
The simulation result of scheme 3: that thermal conductivity of polyurethane foam material is 0.025 w / ( m k ), and the simulation result show that when scheme 3 is adopted, the temperature outside the pipeline is 30.610 deg c, which is low than the ambient temperature of 4.390 deg c, and the polyurethane foam thermal insulation material with the thickness of 17 mm can obtain better thermal insulation effect on the premise of no damage.
Compare with that above four simulated work conditions, the temperature of the outer wall of the pipeline is very close to the temperature of the fluid in the pipeline under the condition of no heat preservation measure, because the pipeline often has the phenomenon of' sweat' in sum, and the thickness required by scheme 1 is the smallest and that required by scheme 2 is the largest in order to obtain the same heat preservation effect.
3, Heat preservation performance comparison
Because the oil temperature of the pipeline has certain floating, according to the simulation method, the oil temperature is - 10 ℃, - 5 ℃, 0 ℃, 5 ℃, 10 ℃, the ambient temperature is 30 ℃, 35 ℃, 40 ℃, according to the set field conditions, the calculation results of the pipeline outer wall temperature under the above four conditions are compared, the results show that bare pipe basically has no insulation performance; Scheme 1, scheme 2 and scheme 3 have the same thermal insulation effect under the theoretical state ( table 1 ); Under the three heat preservation schemes, the pipeline will not appear condensation problem in summer; In ord to obtain that same thermal insulation effect, the thickness required by the nano aerogel thermal insulation felt is the minimum.

According to the construction performance and economic comparison of three kinds of insulation materials ( table 2 ), in terms of construction performance, nano aerogel insulation felt has great advantages, because of its high cost, although the economy is slightly insufficient, but the long service life and less maintenance costs to a certain extent make up for this disadvantage.

4. Conclusion
The simulation analysis and comparison results of three thermal insulation materials show that 10 mm thick nano aerogel thermal insulation felt has the same thermal insulation effect as 25 mm thermal insulation rubber and plastic or 17 mm polyurethane foam thermal insulation materials in terms of thermal insulation performance according to the set field conditions, which can well solve the problem of pipeline " sweating". In addition, the nano aerogel insulation felt coated on the surface of the buried pipeline can effectively reduce the heat loss of the pipeline, protect the frozen soil foundation in cold regions and ensure the long-term safe operation of the pipeline.
The nano aerogel thermal insulation felt has no high requirement on the construction technology, because of its light weight, easy cutting and sewing, can adapt to various shapes of pipelines and equipment thermal insulation, and installation time and labor are less, the transportation cost is lower, and the nano aerogel thermal insulation felt will be popularized in the field of pipeline application in China in the future.