The Economic Thickness of Insulation for Steam Process Distribution Pipelines

Abstract

Steam pipes are very important in engineering application and are widely used. Thermal insulation is one of the most effective energy-conservation measures in hot pipes. One of the primary purposes of insulation is to conserve energy and increase plant profitability by reducing operating expenses.  In existing plants, the planned and conscientious maintenance of insulated hot pipes is required to minimize financial and thermal losses. This seems like a statement of the obvious, and it is. Although an increase in the amount of insulation applied will raise the initial installed cost, but it will reduce the rate of heat loss through the insulation. This paper aims to confirm whether there is an optimal insulation thickness appropriate to the minimum total cost, and to see what the values and facts affecting the value of the minimum cost are. An optimization model is performed depending on Life Cycle Cost analysis. For this purpose, a computer program has been prepared based on the flow chart of the operation procedure overviewed in this paper. The results of Calculations carried out by the computer have given a new concept that is termed as “the critical thermal conductivity of insulation material”, the exceeding of which makes the insulation of pipe a factor that contributes to increase of total cost (ΣC) but not the opposite. The study carried out on steam pipe with outside diameter of 0.1m, steam temperature of 120 °C, steam price of 0.005 $/kg and insulation material price of 175 $/m³ shows that the critical thermal conductivity of insulation material is 0.21 w/(m. °C), the  exceeding of which will not cause  decrease in the expected total cost of steam pipe insulation and the   optimal insulation thickness  can not be achieved. When the thermal conductivity of the insulation material used is less than that of the critical thermal conductivity by 0.10 w/(m.°C), the total cost drops from 9.69 $/(m.year) without insulation to minimum total cost of  5.184 $/(m.year)  with the thermal insulation thickness  of 0.092m. The outside temperature of insulation material drops from 117 to 34.4 °C. The effect of the price of steam generation, the price of insulation material, pipe diameter and temperature of steam on the optimal insulation thickness and critical thermal conductivity of insulation material are overviewed in this paper.

Keywords: Optimum insulation thickness, steam pipe insulation, thermal conductivity