Thermal Insulation Material Necessary and Importance

Process equipment such as a reaction vessel, reboiler, distillation column, evaporator, etc. Or a steam pipe will lose heat to the atmosphere by conduction, convection, and radiation. In such cases, the conservation of heat that is usually from steam and coal is an economic necessity and therefore some form of lagging should be applied to the hot surfaces. 

In furnaces, the surface temperature is reduced substantially by making use of a series of insulating bricks that are poor conductors of heat. 

{tocify} $title={Table of Contents} 

Thermal Insulation is Necessary

i. Insulation is necessary to prevent an excessive flow of costly heat to the surroundings from process units and pipelines in which heat is generated, stored, or conveyed at a temperature above the surrounding temperature. 

ii. To prevent an excessive flow of heat from the outside to materials which must be kept at temperatures below that of the surroundings too. 

iii. To prevent for protection of personnel from skin damage through contact with a very hot and very cold surface. 

iv.  To provide a comfortable/acceptable working environment. The working environment in the vicinity of process units and pipelines carrying hot or cold streams can become uncomfortable and unacceptable if insulation is not provided.

In a chemical plant, steam is transported to process equipment, as per requirement, through steam lines. If the steam lines are not insulated then the loss of heat from these lines to the ambient air may result in condensation of steam, thus lowering the quality of steam and creating operational problems in the equipment in which the steam is admitted. 

The Important requirements of an insulating material

(i) It should have low thermal conductivity. 

(ii) If should withstand working temperature range. 

(iii) If should have sufficient durability and mechanical strength. This includes resistance to moisture and the chemical environment. 

(iv) It should be easy to apply, non-toxic, readily available, and expensive (low basic material cost, installation cost, and maintenance cost).

(v) If should not constitute a fire hazard. 

Low thermal conductivity material

Cork [k =0.025 W/m•K], asbestos (k= 0.10), glass wool (k = 0.024), and 85% magnesia (k = 0.04) are commonly employed lagging materials in the industry. Cork is common in refrigeration plants. 85% magnesia with asbestos and glass wool is widely used for lagging steam pipes. Thin aluminum sheeting is often used to protect the lagging. 

The optimum thickness of insulation

The optimum thickness of insulation is obtained by a purely economic approach. The greater the thickness, the lower the heat loss the greater the initial cost of insulation, and the greater the annual fixed charges. 

It is obtained by a purely economic approach. Increasing the thickness of insulation reduces the loss of heat and thus gives savings in operating costs but at the same time cost of insulation will increase with thickness. The optimum thickness of insulation is the one at which the total annual cost (the sum of values of heat lost and annual fixed charges) of the insulation is minimal. 

Take these Notes is, Orginal Sources: Unit Operations-II, KA Gavhane