The Process Heat Exchangers Engineering Essay

The Process Heat Exchangers Engineering Essay In this part, a full unit of warmth exchanger will be structured including its synthetic and mechanical plan. A warmth exchanger is a gadget worked for productive warmth move between two liquids starting with one medium then onto the next. The medium might be isolated by a strong divider, so the liquids never blend, or the liquids may never be in direct contact. Two liquids of various temperatures will course through the warmth exchanger. Warmth exchangers are broadly utilized in space warming, refrigeration, cooling, power plants, concoction plants, petrochemical plants, oil treatment facilities, and flammable gas preparing. 3.1.1 Classification of Heat Exchanger Warmth exchangers might be characterized by their stream game plan. There are two fundamental stream courses of action which are equal stream and counter-current-stream. In equal stream heat exchangers, the two liquids enter the exchanger at a similar end, and travel in corresponding to each other to the opposite side. In counter-stream heat exchangers the liquids enter the exchanger from furthest edges. Looked at both stream courses of action, the counter current plan is generally effective, in that it can move the most warmth from the warmth move medium. 3.1.2 Types of Heat Exchanger There are numerous kinds of warmth exchanger in industry. The sorts picked dependent on the capacity of the warmth exchanger itself. Picking the correct warmth exchanger requires information on various kind of warmth exchanger just as well as the earth in which the warmth exchanger will work. With adequate information on heat exchanger types and working prerequisites, as well as can be expected be made in enhancing the procedure. Beneath, in Table 3.1 are rundown of types and elements of each warmth exchanger. Table 3.1: Types and Functions of Heat Exchanger in Industry No. Types Capacities 1. Twofold funnel heat exchanger The least complex sort. Use for warming and cooling. 2. Shell and cylinder heat exchanger Utilized for all application. 3. Plate exchanger Use for warming and cooling. 4. Plate-balance exchanger Use for warming and cooling. 5. Winding warmth exchanger Use for warming and cooling. 6. Air cooled Cooler and condenser. 7. Direct contact Cooling and extinguishing. 8. Unsettled vessels Use for warming and cooling. 9. Terminated warmers Use for warming and cooling. Source: Chemical Engineering Design, R.K.Sinnott. 3.1.3 Selections of Heat Exchanger Commonly in the assembling business, a few unique sorts of warmth exchangers are utilized for simply the one procedure or framework to infer the last item. So as to choose a proper warmth exchanger, one would right off the bat consider the structure constraints for each warmth exchanger type. In spite of the fact that cost is frequently the main model assessed, there are a few other significant determination rules which include: High/Low weight limits Warm Performance Temperature ranges Item Mix (fluid/fluid, particulates or high-solids fluid) Weight Drops over the exchanger Liquid stream limit Clean-capacity, upkeep and fix Materials required for development Capacity and simplicity of future extension 3.2 BASIC PRINCIPLES OF DESIGN 3.2.1 Design Criteria for Process Heat Exchangers There are a few standards that a procedure heat exchanger must fulfill are effectively enough expressed on the off chance that we restrict ourselves to a specific procedure. The measures include: The warmth exchanger must meet the procedure necessities. This implies it must impact the ideal change in warm state of the procedure stream inside the permissible weight drops. Simultaneously, it must keep doing this until the following planned shut down for support. The warmth exchanger must withstand the administration states of the earth of the plant which incorporates the mechanical worries of establishment, startup, shutdown, typical activity, crises and upkeep. In addition, the warmth exchanger should likewise oppose erosion by nature, procedures and streams. This is primarily a matter of picking materials of development, however mechanical structure has some impact. The warmth exchanger must be viable, which ordinarily infers picking a setup that licenses cleaning and substitution. So as to do this, the constraints is the situating the exchanger and giving clear space around it. Substitution ordinarily includes tubes and different parts that might be particularly defenseless against consumption, disintegration, or vibration. The expense of the warmth exchanger ought to be reliable with necessities. Which means of the expense here execute to the expense of establishment. Activity cost and cost of lost creation because of exchanger glitch or inaccessible ought to be viewed as before in the plan. The restrictions of the warmth exchanger. Restrictions are on length, distance across, weight and cylinder particulars because of plant necessities and procedure stream. 3.2.2 Structure of the Heat Exchanger The fundamental structure of warmth exchanger is a similar in the case of utilizing hand plan technique or PC structure strategy. The consistent structure of the warmth exchanger plan strategy is appeared in Figure 2.15. From the figure, more clear view and steps of structuring a warmth exchanger can be acquired. Figure 3.1: Basic Logical Structure of Heat Exchanger Design 3.3 CHEMICAL DESIGN 3.3.1 Problem Identification In planning a warmth exchanger underway of 100, 000 metric tons/year of Acrylonitrile, there is just one warmth exchanger exists. Its capacity is to trade the temperature between the stream from Reactor with the temperature from 125 °C to 25 °C and the stream originates from Reboiler 5 from 90 °C to 120 °C. 90.0 0C 125.0 0C 450.0 0C 120.0 0C Figure 3.2: Diagram of shell and cylinder heat exchanger 3.3.2 Determination of physical properties Table 3.2: Physical Properties of the cylinder side liquid (water) Properties Channel Mean Outlet Temperature (0C) 90.0 105 120 Weight (kPa) 70.139 120.82 198.52 Explicit warmth (kJ/kg0C) 4.204 4.224 4.249 Warm conductivity (W/m0C) 0.1154 0.1198 0.1127 Thickness (kg/m3) 0.431 0.623 0.721 Consistency (N sm-2) 3.145 x 10-4 2.677 x 10-4 2.321 x 10-4 Table 3.3: Physical Properties of shell liquid ( process liquid) Properties Normal Temperature, Tave = 287.5 0C Weight (kPa) 150 Explicit warmth (kJ/kg0C) 1.1 Warm conductivity (W/m0C) 0.1553 Thickness (kg/m3) 1.255 Consistency (N sm-2) 4.529 x 10-4 Just the warm structure will be done by utilizing Kerns technique. Since water is destructive, so the cylinder side is allocate. Logarithmic mean temperature, Where, T1 = Inlet shell side liquid temperature T2 = Outlet shell side liquid temperature t1 = Inlet tube side liquid temperature t2 = Outlet tube side liquid temperature In this way, Log mean temperature = 131.4477 0C The genuine temperature contrast is given by, Where, is the temperature amendment factor From Figure 12.19, Chemical Engineering Design, In this way, 0C From Table 12.1(Sinnott 2005), we accept estimation of by and large coefficient, U = 500.0 W/m2.oC. Warmth Load: Warmth move region, Where, Q = heat moved per unit time (W) U = in general warmth move coefficient,(W/m2.oC) Tm = the mean temperature contrast (oC) In this way, = 190.126 m2 3.3.3 Tube-side coefficient Table 3.4: Dimension of Heat-Exchanger tubes Material Carbon Steel External distance across, Dto (mm) 50.8 Length of cylinder Lt (m) 5.0 Internal breadth, Dti (mm) 45.26 BWG number 12.0 Source: Transport Processes and Separation Process Principles, C. J. Geankoplis Warmth move region of a cylinder, At = Ï€DoL = Ï€ (50.8 x 10-3) 5 = 0.798 m2 Number of cylinder, Nt = An/At = 190.126/0.798 = 238.25 = 239 cylinders Cross sectional region of a cylinder = (Ï€Di2)/4 = [ï€ (45.26 x 10-3)2] 4 = 1.6089 x 10-3 m2 By utilizing two passes; Complete cylinder territory, AT = (239/2) (1.6089 x 10-3) = 0.1923 m2 Mass speed, Gs = flowrate/A = 29.96/0.1923 = 155.798 kg/m2.s Reynolds number, Re = [ Gsdi ]/ µ = [ 155.798 x 0.04526 ]/4.529 x 10-4 = 1.557 x 10 4 Prandtl number, = [ 3.1731 x 155.798 ]/0.1553 = 3183.275 Nusselt number, NuD = 0.027 Rea Prb [â µ/ µw]c = 0.027 (1.557 x 10 4)0.8 (3183.275)0.3 x 1 = 685.578 Stanton number, St = NuD/[Re(Pr)] = 685.578/[1.557 x 10 4 x 3183.275 ] = 1.383 x 10-5 Warmth Transfer factor, jh = St Pr0.67 = 1.383 x 10-5 ( 3138.275 )0.67 x 1 = 3.045 x 10-3 Cylinder side warmth move coefficient, hey = 2329.599 W/m2.0C 3.3.4 Shell side coefficient 1.25 triangular pitch was picked to ascertain the pack breadth. From table 12.4 (Sinnott 2005), constants esteem for 2 cylinder passes condition is K1 = 0.249 and n1 = 2.207 Group width, Db = Dto (Nt/K1) 1/n1 = 50.8 ( 239/0.249)1/2.207 = 1122.575 mm Get through gliding head type was the best determination. From Figure 12.10 (Sinnott 2005), pack distance across freedom is 95 mm. Shell measurement, Ds = 1122.575 + 95 = 1217.575 mm For choosing astound dividing, the ideal separating picked is 0.2 occasions the shell distances across. Astound dispersing, B = 0.2 Ds = 0.2 (1217.575) = 243.515mm Cylinder pitch pt = 1.25 Do = 1.25 (50.8) = 63.5mm Cross-stream zone, = 0.0593 m2 Mass speed, Gs = Ws/As = 47.7672/0.0593 = 805.518 kg/m2.s Comparable measurement, = 36.07 mm Shell-side warmth move coefficient, ho Reynolds number, Re = [ Gsdi ]/ µ = [ 805.518 x 36.07 x 10-3 ]/2.677 x 10-4 = 1.0854 x 10 5 Prandtl number, = [2.677 x 10-4 (2.4923 x 103) ]/0.1553 = 4.296 Note that 45% astound cut has been picked, disregard the consistency adjustment term. From Figure 12.29 (Sinnott, 2005), jh = 2.8 x 10-3 = 1640.892 W/m2.0C 3.3.5 Overall Coefficient Table 3.5: Dimensions in generally speaking coefficient Material Carbon steel Warm conductivity of carbon steel Kw = 45 W/m0C The fouling factor for cooling water shrouded 5000 W/m2.0C The fouling factor for watery salt arrangements h0 =3000 W/m2.0C Source: Chemical Engineering Design, R.K.Sinnott. The connection between in general coefficient and individual coefficients is given by: UO = 583.359 W/m2.0C Well a