Jacketed Vessel

Chemical Engineering Department

TUTORIAL NO.

JACKETED VESSEL(MECHANICAL DESIGN)

TUTORIAL NO.

JACKETED VESSEL(MECHANICAL DESIGN) 1



(A) INTRODUCTION : Jacketed vessel is pressure vessel to carry out reactions under controlled condition. The reaction vessel requires cover or head that can be fitted tightly to the vessel shell. So the pressure and temperature can be maintained as desired inside. Capacities of the vessel vary from 100 lit to 1500 lit. and diameter may vary from 50 cm to 250 cm. Head used for vessels are shallow-dished, torispherical or elliptical. Several nozzles inlet, Outlet, sight glass and light glass, Thermo well, hand holes and man holes are provided to satisfy the process requirements. Jacket is used to circulate heating or cooling media. (B) AGITATION : Agitation of the content of reaction vessel increasing heat and mass transfer. Paddle agitator, turbine agitator and propeller agitator are most widely used. The agitator with drive assembly must be located at the top of the vessel with preferably in independent supporting structure. (C) HEATING/COOLING: If the heating is required then the hot fluid is supplied in the jacket. Jacket surrounds the vessel wall. Fluid such as hot oil, hot water or air, molten salt mixture, special organic compounds such as therminol and dow- therm are used as heating media. If cooling is desired than air, liquid ammonia, cold water or brine, oil can be used. The space between the vessel wall and the jacket shell should be narrow for obtaining good heat transfer rates. Various types of jacket are used for this purpose. Special types of jacket such as channel and coiled jacket provides high velocity of circulating fluid and hence high heat transfer rates. (D) DESIGN PROCEDURE : Design is based on pressure and temperature condition. This types of reaction vessel is nothing but pressure vessel with heads and nozzles. Due to jacket there is external pressure on the vessel wall. So the vessel is designed for both internal & external pressure and the higher value of wall thickness is accepted. A plain jacket is simplest arrangement for heating or cooling. In most cases jacket extends over the base of the reactor and provision must be made for applying the vessel as well as for removing fluid from the jacket.

(1) Thickness of shell : For the cylindrical shell :[ i ] For Internal pressure : Design pressure = Internal pressure + 10% of internal pressure Shell thickness (t) = p Di /(

2f J - p) = p Do /(2f J + p)= p D /(

2f J)

Where p= Design pressure D = Mean diameter Di = Internal diameter D0 = Outside Diameter J = Joint efficiency ƒ = Design or permissible stress at design temperature 2



Value of permissible stress for different material of construction will be different. [ ii ] For External pressure :Design pressure = Pressure in the jacket +10% of pressure in the jacket. First calculate the critical external pressure using above shell thickness calculated for internal pressure : pc = 2.42 E (t/D0)5/2 /{(1- µ 2)3/4[(L/D0) – 0.45 (t/D0)1/2]} Where, L= Unsupported length of vessel E= Modulus of elasticity µ =poison’s ratio Now allowable external working pressure, Pa = pc /4 Now, Pa must be grater than design pressure and if Pa < design pressure then increase the shell thickness until this condition satisfies.

(2) Stiffening ring : This ring can provide considerable saving in weight and material. Rings are attached to the inside/outside surface of the shell. They extend over the whole circumference and serve the purpose of end support. T-beams and flat plate ring are simple, light and effective. Now effective length of vessel is considered the length between stiffening ring . The stiffening ring must have movement of interna given by I = pc Do3L/ (24 E)

The value of ‘I’ may be reduced by about 30% to taken into account the resistance of the shell.

(3) Thickness of jacket : Internal design= Pressure inside jacket +10% of pressure inside the jacket tj = pDi /(2 f J - p) Where Di = Jacket internal diameter.

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(4) Head thickness : For Torispherical head :th = p Rc W /(2 f J ) Where Rc = Crown radius W = Stress intensification factor = (1/4) [3 + ( Rc / R1) ] Ri = Knuckle radius Above head thickness should be checked for external pressure also. th = 4.4 Rc

(1 - µ2 ) p /( 2 E )

Where P=Design external pressure(Pressure inside the jacket) ============================* * * * * * * =========================

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Jacketed Vessel

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