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Making Decisions with Insulation

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Making Decisions with Insulation Powered By Docstoc
					Topic : Insulation Material
Name : Abhaykumar J. Choudhari
E-mail : ajchoudhary@dtps.bses.com



                                           C 12/6 , BSES NAGAR
                                           Dahanu TPS. , Dahanu Road .
                                           Dist : Thane , Pin :401 608 (M.S)




How you select insulation material and on what basis a decision is made concerning material
selection and costs.



                                           Index

 Sr.no   Topic                                                                 Page no.
   1     Introduction                                                             1
   2     Functions of Insulation                                                  1
   3     Characteristics of Insulation                                            2
   4     Insulation Types, Forms & Finishes                                       4
   5     Latest Insulating material used in process plant                         7
   6     A Brief Look at Theory for insulation calculation                       8-9
   7     Major points in Selection of Insulation                                10-15
   8     Design and Selection Tools                                              16
   9     Summary                                                                 17
  10     Annexure-I Table 1: Economic Indoor Insulation Thickness (Metric        18
         Units)
  11     Annexure-II Table 2: Economic Outdoor Insulation Thickness               19
         (Metric Units)
  12     Annexure-III Dew point temperature table                                20
  13     Annexure-IV Example of Economic Thickness Determination:                21
  14     Annexure-V Example of Outer Surface Temperature Determination:          22
  15     Annexure-VI Practical Example of process condition                     23-24




                                      Page 0
1. Introduction :

What is Thermal Insulation?


Insulation    - From the Latin word for island (insula). Insulation is the noun describing
material which insulates (cuts off) heat (or electricity) from its surroundings. It is a scientific
noun and was first recorded in 1870.

        Insulation is defined as a material or combination of materials which retard the flow of heat.
The materials can be adapted to any size, shape or surface. A variety of finishes are used to protect
the insulation from mechanical and environmental damage, and to enhance appearance.

         Many people overlook the importance of insulation in the process industry .For industrial
facilities, such as power plants, refineries, and paper mills, mechanical thermal insulations are
installed to control heat gain or heat loss on process piping and equipment, steam and condensate
distribution systems, boilers, smoke stacks, bag houses and precipitators, and storage tanks. While
placing insulation onto a pipe is fairly easy, resolving issues such as what type of insulation to use
and how much is not so easy. Insulation is available in nearly any material imaginable. The most
important characteristics of any insulation material include a low thermal conductivity, low
tendency toward absorbing water, and of course the material should be inexpensive. In the
process industry, the most common insulators are various types of calcium silicate or fiberglass.
Calcium silicate is generally more appropriate for temperatures above 225 0C (437 0F), while
fiberglass is generally used at temperatures below 225 0C.

2. Functions of Insulation
Insulation is used to perform one or more of the following functions:

    •   Reduce heat loss or heat gain to achieve energy conservation.
    •   Protect the environment through the reduction of CO2 , NOx and greenhouse gases.
    •   Control surface temperatures for personnel and equipment protection.
    •   Control the temperature of commercial and industrial processes.
    •   Prevent or reduce condensation on surfaces.
    •   Increase operating efficiency of heating/ventilation/cooling, plumbing, steam, process and power
        systems.
    •   Prevent or reduce damage to equipment from exposure to fire or corrosive atmospheres.
    •   Assist mechanical systems in meeting USDA (FDA) criteria in food and pharmaceutical plants.
    •   Reduce noise from mechanical systems.

Understanding Heat Flow/Heat Transfer

In order to understand how insulation works, it is important to understand the concept of heat flow or heat
transfer. In general, heat always flows from warmer to cooler surfaces. This flow does not stop until the
temperature in the two surfaces is equal. Heat is 'transferred' by three different means:

conduction,




                                              Page 1
convection

radiation.

Insulation reduces the transference of heat.

Physical Properties

    •   Mass Insulation

        For mass insulation types, the most important physical property is thermal conductivity. Materials with
        low thermal conductivity allow less heat to be transferred per unit time, per unit temperature
        difference per inch of thickness. All other items being the same, materials with lower thermal
        conductivities are better insulators. Commercially available mass insulations have thermal
        conductivities at 75°F mean temperature less than 0.5 Btu in/(hr, S.F., °F).

    •   Reflective Insulation

        For reflective insulation types, the important physical property is low surface emittance. Surfaces with
        low emittance have high reflectance. Reflective insulations have emittance values in the range of 0.04
        to 0.1.


3. Characteristics of Insulation
Insulations have different properties and limitations depending upon the service, location, and required
longevity of the application. These are taken into account by engineers when considering the insulation needs
of an industrial or commercial application.

    •   Thermal Resistance (R) (F ft2 h/Btu)

        The quantity determined by the temperature difference, at steady state, between two defined surfaces
        of a material or construction that induces a unit heat flow rate through a unit area. A resistance
        associated with a material shall be specified as a material R. A resistance associated with a system
        or construction shall be specified as a system R.

    •   Apparent Thermal Conductivity (ka) (Btu in./h ft2 F)

        A thermal conductivity assigned to a material that exhibits thermal transmission by several modes of
        heat transfer resulting in property variation with specimen thickness or surface emittance.




    •   Thermal Conductivity (k) (Btu in./h ft2 F)

        The time rate of steady state heat flow through a unit area of a homogenous material induced by a
        unit temperature gradient in a direction perpendicular to that unit area. Materials with lower k factors
        are better insulators.

    •   Density (lb/f3) (kg/m3)

        This is the weight of a specific volume of material measured in pounds per cubic foot (kilograms per
        cubic meter).

    •   Surface Burning Characteristics


                                               Page 2
    These are comparative measurements of flame spread and smoke development with that of select
    red oak and inorganic cement board. Results of this test may be used as elements of a fire-risk
    assessment which takes into account all of the factors which are pertinent to an assessment of the
    fire hazard or fire risk of a particular end use.

•   Compressive Resistance

    This is a measure of the material to resist deformation (reduction in thickness) under a compressive
    load. It is important when external loads are applied to an insulation installation. Two examples are
    deforming the insulation on a pipe at a Clevis type hanger due to the combined weight of the pipe and
    its contents between the hangers and....Resistance of an insulation to compress on an outdoor
    rectangular duct due to heavy mechanical loads from external sources such as wind, snow, or
    occasional foot traffic.

•   Thermal Expansion/Contraction and Dimensional Stability

    Insulation systems are installed under ambient conditions that may differ from service conditions.
    When the operating conditions are imposed, metal surfaces may expand or contract differently from
    the insulation and finish applied. This can create openings and parallel heat flow and moisture flow
    paths that can degrade system performance.

    Long term satisfactory service requires that the insulating materials, closure materials, facings,
    coating, and accessories withstand the rigors of temperature, vibration, abuse, and ambient
    conditions without adverse loss of dimensions.

•   Water Vapor Permeability

    This is the time rate of water vapor transmission through unit area of flat material of unit thickness
    induced by unit vapor pressure difference between two specific surfaces, under specified temperature
    and humidity conditions. It is important when insulation systems will be operating with service
    temperatures below the ambient air. Materials and systems with low water vapor permeability are
    needed in this service.

•   Cleanability

    Ability of a material to be washed or otherwise cleaned to maintain its appearance.




•   Temperature Resistance

    Ability of a material to perform its intended function after being subjected to high and low
    temperatures which the material might be expected to encounter during normal use.

•   Weather Resistance

    Ability of a material to be exposed for prolonged periods of time to the outdoors without significant
    loss of mechanical properties.

•   Abuse Resistance

    Ability of a material to be exposed for prolonged periods of time to normal physical abuse without
    significant deformation or punctures.

•   Ambient Temperature


                                         Page 3
        The dry bulb temperature of surrounding air when shielded from any sources of incident radiation.

    •   Corrosion Resistance

        Ability of a material to be exposed for prolonged periods of time to a corrosive environment without
        significant onset of corrosion and the consequential loss of mechanical properties.

    •   Fire Resistance/Endurance

        Capability of an insulation assembly exposed for a defined period of exposure to heat and flame (fire)
        with only a limited and measurable loss of mechanical properties. Fire endurance is not a
        comparative surface burning characteristic for insulation materials.

    •   Fungal Growth Resistance

Ability of a material to be exposed continuously to damp conditions without the growth of mildew or mold.


4. Insulation Types, Forms & Finishes:
The three basic types of insulating materials for industrial use are:

    1. thin (less than 20 micrometers), low-density (less than 12 lb/ft3) fibers made from organic or inorganic
       materials;
    2. cellular material in closed or open cell form made of organic or inorganic material; and
    3. flaked or granular inorganic materials bonded in the desired form.

In most cases, glass (silica), mineral wool, high alumina, mulite, or zirconia are the base materials and can be
used to temperatures as high as 2900°F. This class of materials has a lower density that varies from 4 lb/ft3
to 12 lb/ft3 and offers higher thermal resistance compared to firebricks or insulating firebricks. In all cases,
thermal conductivity of the insulation increases significantly as temperature increases.

Mass Insulation Types

    •   Fibrous Insulation

        Composed of air finely divided into interstices by small diameter fibers usually chemically or
        mechanically bonded and formed into boards, blankets, and hollow cylinders.

            o Fiber glass or mineral fiber
            o Mineral wool or mineral fiber
            o Refractory ceramic fiber
    •   Cellular Insulation

        Composed of air or some other gas contained within a foam of stable small bubbles and formed into
        boards, blankets, or hollow cylinders.

            o   Cellular glass
            o   Elastomeric foam
            o   Phenolic foam
            o   Polyethylene
            o   Polyisocyanurates
            o   Polystyrene
            o   Polyurethanes
            o   Polyimides



                                              Page 4
   •   Granular Insulation

       Composed of air or some other gas in the interstices between small granules and formed into blocks,
       boards, or hollow cylinders.

           o   Calcium silicate
           o   Insulating finishing cements
           o   Perlite

Forms of Insulation

   •   Board

       Rigid or semi-rigid self-supporting insulation formed into rectangular or curved shapes.

           o   Calcium silicate
           o   Fiber glass or mineral fiber
           o   Mineral wool or mineral fiber
           o   Polyisocyanurates
           o   Polystyrene
   •   Block

       Rigid insulation formed into rectangular shapes.

          o    Calcium silicate
          o    Cellular glass
          o    Mineral wool or mineral fiber
          o    Perlite
   •   Sheet

       Semi-rigid insulation formed into rectangular pieces or rolls.

           o Fiber glass or mineral fiber
           o Elastomeric foam
           o Mineral wool or mineral fiber
           o Polyurethane
   •   Flexible Fibrous Blankets

       A flexible insulation used to wrap different shapes and forms.

           o Fiber glass or mineral fiber
           o Mineral wool or mineral fiber
           o Refractory ceramic fiber
   •   Pipe and Fitting Insulation Pre-formed insulation to fit piping, tubing and fittings
           o Calcium silicate
           o Cellular glass
           o Elastomeric foam
           o Fiber glass or mineral fiber
           o Mineral wool or mineral fiber
           o Perlite
           o Phenolic foam
           o Polyethylene
           o Polyisocyanurates
           o Polyurethanes
   •   Foam




                                               Page 5
       Liquid mixed at the time of application which expands and hardens to insulate irregular areas and
       voids.

          o Polyisocyanurates
          o Polyurethane
   •   Spray Applied Insulation

       Liquid binders or water introduced to an insulation while spraying on to flat or irregular surfaces for
       fire resistance, condensation control, acoustical correction and thermal insulation.

          o Mineral wool or mineral fiber
   •   Loose fill Granular insulation used for pouring expansion joints.
          o Mineral wool or mineral fiber
          o Perlite
          o Vermiculite
   •   Cements (Insulating and Finishing Muds)

       Produced with mineral wool and clay insulation, these cements may be hydraulic setting or air drying
       types.

   •   Flexible Elastomeric Foam

       Foam sheets and tubing insulation containing vulcanized rubber.

Insulation Finishes

Insulation finishes are important because the ability of an insulation system to perform as designed and
specified is dependent upon protection from moisture, weather, chemical and mechanical damage. Insulation
can also be used to enhance system appearance.

   •   Weather Barriers

       Protect the insulation from rain, snow, ice, sunlight, ultraviolet degradation, ozone and residues of
       chemical compounds in the atmosphere.

          o Mastic
          o Metal
          o Plastic
          o Roofing felt
   •   Vapor Retarders

       Retard the passage of moisture vapor from the atmosphere to the interior of the insulation system.

          o CPVC
          o FRP
          o Laminated foil-scrim membranes
          o Mastic
          o Metal
          o Plastic
          o PVC
          o Reinforced polyester resin
   •   Mechanical Abuse Protection

       Rigid jacketing provides protection against mechanical abuse from personnel, equipment, machinery,
       etc.



                                             Page 6
           o Metal
           o Plastic
    •   Appearance Chosen primarily for appearance value in exposed areas.
           o Fabrics
           o Laminate foil/scrim membranes
           o Painted metal
           o Paints
           o PVC


5. Latest Insulating material used in process plant
Since the dawn of civilization, human beings have recognized the need for insulation. Pre-historic man
clothed himself with wool and skins from animals, and built homes of wood, stone, earth, and other materials
to protect against the cold in winter and the heat in summer. Over the years, man discovered:

    •   Asbestos

        Asbestos was first discovered by the ancient Greeks and Romans and was used extensively in
        containers because of its resistance to heat and fire. More recently, a pipe insulation made from
        corrugated layers of asbestos paper was developed for hot applications, i.e. Air Cell pipe insulation.

    •   Steam Baked Portuguese Cork

        The Romans used cork for insulation. They used it in shoes to keep their feet warm. As
        industrialization expanded, cork was used as an insulation for ice houses. Blocks of ice were cut from
        frozen lakes in winter and stored in cork-lined ice houses for use in summer. When mechanical
        refrigeration came into use, steam baked cork board was used to insulate pipes and equipment.




    •   Rock Wool

        One of the first users were the natives of the Hawaiian Islands who used rock wool to blanket their
        huts. The fibers came from volcanic deposits where escaping steam had broken the molten lava into
        fluffy fibers.

    •   Man-Made Rock Wool

        This was developed in the early industrialization period. Steam was injected into molten slag, a by-
        product from iron furnaces. It has been widely used for both building and industrial insulation. As
        more and more uses were found, rock wool was modified and preformed into different shapes such
        as pipe insulation.

    •   Magnesia

        A now obsolete material used for many years was 85 percent magnesia. This material was similar to
        the calcium silicate used today but had a lower maximum use temperature and contained asbestos
        fibers as a reinforcing agent.

    •   * High-Fiber-Content Felt/Paper

        Materials made from layers of high-fiber-content felt or paper, with layers of asphalt saturated felt
        formerly were used on moderate-to- cold temperature applications.




                                             Page 7
Today, materials manufactured from fiber glass, ceramic, mineral wool, calcium silicate, foamed plastic, glass,
and other substances are used in many shapes and forms



    6. A Brief Look at Theory for thickness calculation:
  The most basic model for insulation on a pipe is shown below. R1 and R2 show the inside and
outside radius of the pipe respectively. R3 shows the radius of the insulation. Typically when
dealing with insulations, engineers must be concerned with linear heat loss or heat loss per unit
length.




Generally, the heat transfer coefficient of ambient air is 40 W/m2 K. This coefficient can of course
increase with wind velocity if the pipe is outside. A good estimate for an outdoor air coefficient in
warm climates with wind speeds under 15 mph is around 50 W/m2 K. The total heat loss per unit
length can then be calculated by:




                                                                         (2)


             Since heat loss through insulation is a conductive heat transfer, there are instances when
adding insulation actually increases heat loss. The thickness at which insulation begins to decrease
heat loss is described as the critical thickness. Since the critical thickness is almost always a few
millimeters, it is seldom (if ever) an issue for piping. Critical thickness is a concern however in
insulating wires. Figure shows the heat loss vs. insulation thickness for a typical insulation. It's easy
to see why wire insulation is kept to a minimum as adding insulation would increase the heat
transfer. ( heat loss vs insulation thickness Fig )




                                             Page 8
7. Major points in Selection of Insulation:
  Three major factors play an important role in determining insulation type and thickness. Here,
we'll focus on resolving the thickness issue since many manufacturing facilities have a "standard"
type of insulation that they use. The three key factors to examine are:


1. Economics
2. Safety
3. Process Conditions


  Each situation must be studied to determine how to meet each one of these criteria. First, we'll
examine each aspect individually, then we'll see how to consider all three for an example.



Economics:

      Economic thickness of insulation is a well documented calculation procedure. The calculations
typically take in the entire scope of the installation including plant depreciation to wind speed. Data


                                          Page 9
charts for calculating the economic thickness of insulation are widely available. Below are
economic thickness tables that have been adapted from Perry's Chemical Engineers' Handbook:

Table 1: Economic Indoor Insulation Thickness (Metric Units) Annexure - I

Table 2: Economic Outdoor Insulation Thickness (Metric Units) Annexure – II

Example of Economic Thickness Determination:        Annexure - IV

Safety:

   Pipes that are readily accessible by workers are subject to safety constraints. The recommended
safe "touch" temperature range is from 130 0F to 150 0F (54.4 0C to 65.5 0C). Insulation
calculations should aim to keep the outside temperature of the insulation around 140 0F (60 0C). An
additional tool employed to help meet this goal is aluminum covering wrapped around the outside of
the insulation. Aluminum's poor thermal conductivity of 0.025 W/m K makes it a good choice
for this application. Typical thickness of aluminum used for this purpose ranges from 0.2 mm to
0.4 mm. The addition of aluminum adds another resistance term to Equation 1 when calculating the
total heat loss:




                                                                                       (3)

However, when considering safety, engineers need a quick way to calculate the surface temperature
that will come into contact with the workers. This can be done with equations or the use of charts.
We start by looking at another diagram:




                                        Page 10
At steady state, the heat transfer rate will be the same for each layer:




                                                                                               (4)



Rearranging Equation 4 by solving the three expressions for the temperature difference yields:




                                                                                   (5)



Each term in the denominator of Equation 5 is referred to as the "resistance" of each layer. We will
define this as Rs and rewrite the equation as:



                                                                                   (6)



         Since the heat loss is constant for each layer, use Equation 4 to calculate Q from the bare
pipe, then solve Equation 6 for T4 (surface temperature). Use the economic thickness of your
insulation as a basis for your calculation, after all, if the most affordable layer of insulation is safe,
that's the one you'd want to use. If the economic thickness results in too high a surface temperature,
repeat the calculation by increasing the insulation thickness by 1/2 inch each time until a safe touch
temperature is reached.


                As you can see, using heat balance equations is certainly a valid means of estimating
surface temperatures, but it may not always be the fastest. Charts are available that utilize a
characteristic called "equivalent thickness" to simplify the heat balance equations. This correlation
also uses the surface resistance of the outer covering of the pipe. Figure 4 shows the equivalent


                                           Page 11
thickness chart for calcium silicate insulation. Table 5 shows surface resistances for three popular
covering materials for insulation:




    With the help of Figure 4 and Table 5 (or similar data for another material you may be dealing
with), the relation:


                                        Page 12
                                                                (7)

can be used to easily determine how much insulation will be needed to achieve a specific surface
temperature. Let's look at an example to illustrate the various uses of this equation.

Example of Outer Surface Temperature Determination -- Annexure - V



Process Conditions:

       The temperature of a fluid inside an insulated pipe is an important process variable that must
be considered in many situations. Consider the length of pipe connecting two pieces of process
equipment shown below:




     In order to predict T2 for a given insulation thickness, we first make the following assumptions:

1.   Constant fluid heat capacity over the fluid temperature range
2.   Constant ambient temperature
3.   Constant thermal conductivity for fluid, pipe, and insulation
4.   Constant overall heat transfer coefficient
5.   Turbulent flow                                                         inside pipe
6.   15 mph wind for                                                        outdoor calculations




                                           Page 13
Another heat balance equation yields:




                                                                       (9)

Setting Equation 8 equal to Equation 9 and solving for T2 yields:



                                                                         (10)

Equation 10 provides another useful tool for analyzing insulation and its impact on a process.

   One example may be the importance of designing insulation thickness to prevent condensation on
cold lines. Usually, when we hear the word "insulation" we instantly think of hot lines. However,
there are times when insulation is used to prevent heat from entering a line. In this situation, the dew
point temperature of the ambient air must be considered. Dewpoint temperatures as a function of
relative humidity and dry bulb temperatures. Dew point temperature table - ANNEXURE - III

It is crucial that sufficient insulation is added so that the outer temperature of the insulation
remains above the dewpoint temperature. At the dewpoint temperature, moisture in
the air will condense onto the insulation and essentially ruin it.

8. Design and Selection Tools:
        The cost of an insulation material relates to its temperature capability. Hence, insulation and
refractory systems are designed to include several layers of different materials that offer optimum
economic performance. Selecting the most economical system requires consideration of its cost
compared to potential savings from reduction of heat losses. In some cases, the most economical
thickness may not meet regulatory requirements for the safety of personnel and property. In such
cases, appropriate design and materials should be used. In other cases, thickness may be reduced
when there is a danger of exceeding the limiting refractory or insulating temperature.

        A number of tools and design methods are available for selecting the most economical or
appropriate refractories or insulation. For example, 3E Plus Insulation Thickness software,
developed jointly by DOE's Office of Industrial Technologies (OIT) and the North American
Insulation Manufacturer's Association (NAIMA), can be used to calculate and select the insulation
thickness for a variety of conditions.




8. Summary:



                                          Page 14
          There are many factors to consider when thinking about insulation. Insulation          save
money      for certain, but it can also be effective as a safety and process control device.
Insulation can be used to regulate process temperatures, protect workers from serious injury, and
save thousands of dollars in energy costs.

         One should never overlook it's usefulness. It's also bad practice to consider only one of the
important factors discussed in this article. The key is to consider all factors that will be affected by
installing insulation on a pipe or any other piece of equipment .




                                          Page 15
     Annexure – I




Page 16
Annexure – II




Page 17
Annexure – III




 Page 18
                                       Annexure - IV
                 Example of Economic Thickness Determination:

   Using the tables above, assuming a 6.0 in pipe at 500 0F in an indoor setting with an energy cost
of $5.00/million Btu, what is the economic thickness?


  Answer: Finding the corresponding block to 6.0 in pipe and $5.00/million Btu energy costs, we
see temperatures of 250 0F, 600 0F, 650 0F, and 850 0F. Since our temperature does not meet 600 0F,
we use the thickness before it. In this case, 250 0F or 1 1/2 inches of insulation. At 600 0F, we
would increase to 2.0 inches of insulation.
  Economic thickness charts from other sources will work in much the same way as this example.




                                         Page 19
                                        Annexure - V

Example of Outer Surface Temperature Determination:

  Your supervisor asks you to install insulation on a new pipe in the plant. Recently, two workers
suffered severe burns while incidentally touching the new piping so safety is of primary concern. He
instructs you to be sure that this incident does not repeat itself. The pipe contains a heat transfer
fluid at 850 0F (454 0C). The ambient temperature is usually near 85 0F (29.4 0C). After checking
the supplies that you have available, you notice that you have calcium silicate insulation and
aluminum available for covering. You would like to insulate the 16 inch pipe for a surface
temperature of 130 0F.




Tsurface - Tambient = 130 0F - 85 0F = 45 0F, from Table 5 we estimate a Rs value for aluminum at
0.504 h ft2 0F/Btu (0.089 m2 0C/W).
Taverage = (850 0F + 85 0F)/2 = 467.5 0F (242 0C), from Figure 1 we estimate a thermal conductivity
of 0.0365 Btu/h ft 0F (0.0703 W/m 0C) for calcium silicate insulation.



Equivalent Thickness = 3.5 in (89 mm)

From Figure 4 above, an equivalent thickness of 3.5 in corresponds to an actual thickness of 3.0 in of
insulation.




                                         Page 20
                                       Annexure - VI
                             Practical Example of process condition




   In the figure above, a typical reactor feed preheater (interchanger) is shown. The heat exchanger
resides on the first level of the structure while the reactor is on the second level. During
construction, stream 2 was not insulated because it runs from the exchanger directly to the ceiling
away from workers so it posed no safety risk. The reaction is endothermic, so heat is supplied by a
Dowtherm jacket surrounding the vessel. The equivalent length of the pipe containing stream 2 is
100 meters. A recent rise is fuel oil costs (which is used to heat the Dowtherm) has prompted the
company to search for ways to conserve energy. With the data provided below, you recognize an
opportunity for energy savings. Any increase in the reactor feed temperature will reduce the reactor
duty and save money. What is the current reactor entrance temperature compared with the entrance
temperature after applying the economic insulation thickness to the pipe?

Data:
Calcium silicate insulation
Temperature of stream 2 exiting the heat exchanger is 400 0C (752 0F)
Ambient temperature is 23.8 0C (75 0F)
Mass flow = 350,000 kg/h (771,470 lbs/h)
Rinside pipe = R1 = 101.6 mm (2.0 in)
Routside pipe = R2 = 108.0 mm (2.125 in)
Thermal conductivity of pipe = kpipe = 30 W/m K (56.2 Btu/h ft 0F)
Ambient air heat transfer coefficient = ho = 50 W/m2 K (8.8 Btu/h ft2 0F)
Fluid heat capacity = Cpfluid = 2.57 kJ/kg K (2.0 Btu/lb 0F)
Fluid thermal conductivity = kfluid = 0.72 W/m K (1.35 Btu/h ft 0F)
Fluid viscosity = ufluid = 5.2 cP
Energy costs = $4.74/million kJ ($5.00/million Btu)
Equivalent length of pipe = 100 meters (328 feet)




                                         Page 21
Calculations:




Temperature difference with insulation is nearly 2 0C. While this doesn't sound too dramatic,
consider the energy savings over one year with the insulation:

Q = mass flow x Cpfluid x temperature difference
Q = (350,000 kg/h)(2.57 kJ/kg K)(2.0K) = 1799000 kJ/h
1799000 kJ/h x 8760 hours/year = 15,760 million kJ/year
15,760 million kJ/year x $4.74/million kJ = $74,700 per year

By insulating the pipe, energy costs have decreased by nearly $75,000 per year

References: Perry's Chemical Engineers' Handbook




                                        Page 22

				
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