Research On Heat Dissipation Performance Of Thermal Steam Pipeline Insulation And Its Impact On Economy

In the context of gradually replacing coal-fired small boilers,vigorously developing central heating,and increasing the heating radius of the heating network to promote energy saving and emission reduction,the thermal insulation performance of the thermal insulation layer has become an important factor determining the energy efficiency of the heating network.In practice,it is found that the soft insulation layer made of rock wool,glass wool and other materials will have partial damage,material aging and structural variation as the number of years of operation increases,which makes the insulation performance of the insulation layer deteriorate.In this paper,the deterioration characteristics of soft and hard insulation layers and their influencing factors and mechanisms are studied,and the effects of deterioration of insulation on the economy and economic thickness design of insulation layers are also studied.This is of great significance for evaluating the thermal insulation performance of the online heating pipeline and improving the heating radius and heating efficiency of the heating network.Firstly,the thermal insulation performance of soft and hard insulation pipelines with in-service operation years between 4 and 18 years were tested by on-site mesurement to study the variation of insulation performance of soft and hard insulation layers with the number of years of operation.The enthalpy drop method and the new-old surface temperature difference comparison method were used in on-site test,and the TPS method was used to test the thermal conductivity of the soft insulation material samples from 0 to 14 years.The test results show that the surface temperature difference of the soft insulation layer is larger,the natural convection is stronger,and the partial damage and structural variation are more than the hard.The thermal insulation performance is more unstable than the hard insulation layer both on the time scale and spatial scale.The thermal conductivity of soft insulation materials increases with the number of years of operation,but the material aging cannot fully explain the deterioration of insulation performance.Secondly,the numerical simulation method was used to study the effects of material aging,structural eccentricity and bottom hollowing on the performance deterioration of the insulation layer.The results show that the thermal conductivity increasement of the soft insulation material is the main reason for the deterioration of the thermal insulation performance.The structural eccentricity increases the surface temperature difference of the thermal insulation layer,and the partial heat dissipation increases.The bottom hollow interlayer of the thermal insulation layer causes the temperature at the bottom of the insulation layer to rise.For a typical pipeline tested on-site,these three mechanisms increase the heat dissipation of insulation layer by 44%,9%,and 12%,respectively.For the thermal insulated pipeline,the main heat transfer nechannism in the air interlayer is radiative heat transfer;for the cold insulated pipeline,the main heat transfer mechanism in the air interlayer is convection heat transfer.The numerical simulation model considering material aging and structural variation is in good agreement with the test results of the old and new surface temperature difference method.Finally,combined with the thermal conductivity test data and simulation results,the effects of material aging and structural variation on economic thickness design of soft insulation are studied.The results show that the economic thickness of the insulation layer will increase after considering the deterioration of the insulation layer inevitably.Although the annual average cost reduction is not significant,the heat loss can be reduced by 15.4%,which can bring huge energy and environmental economic benefits.Due to the higher purchase price,the average annual cost of using a hard insulation layer is slightly higher than that of a soft insulation layer.However,the longer the design life and the use time of the insulated pipeline,the advantage of the lower annual average heat loss of the hard insulation layer is more prominent.