Steam Heating in Jackets

The dynamics of the jacket are more complex for the case of steam heating. The model representation of the jacket steam heating process is shown in Fig. 3.5. 

The saturated steam density, pj, depends on the jacket temperature, Tj, in the first approximation in accordance with the Ideal Gas Law and hence 

The jacket steam pressure, Pj, is itself a function of the jacket steam temperature, Tj, as listed in steam tables or as correlated by the Antoine equation for vapour pressure, where 

A and B are the Antoine steam constants and Tj abs is the absolute steam temperature. 

The determination of the steam density, pj, therefore requires the simultaneous solution of two algebraic equations. This represents an IMPLICIT algebraic loop and cannot be solved within a simulation program without the incorporation of a trial and error convergence procedure. 

Combining the two equations for steam density and pressure gives an implicit equation requiring a numerical root estimation. 

---

Premix is heated under vacuum to remove sufficient water to give a clear, dark amber-coloured viscous solution of the cellulose. Typically the solutions contain 10 to 18% cellulose. The evaporation of water from premix to make solution is achieved in a wiped thin film evaporator such as a Filmtruder (from Buss-SMS) (see Fig. 5.2). This is a long vertical cylindrical vessel with steam heating in jackets around the vessel. A shaft down the centre of the vessel with blades attached to its circumference is rotated to smear the material around the heated surface to promote the evaporation process and to transport the solution down the vessel. The evaporator vessel is operated under vacuum to reduce the temperature (circa 90 to 120°C) at which the water evaporates. This is important because the amine oxide solvent in solution can undergo an exothermic degradation process if it is overheated. 

Figure 3.5. Model representation of steam heating in the jacket.

The reaction section consists of the high pressure reactors filled with catalyst, and means to take away or dissipate the high heat of reaction (300-500 Btu/lb of olefin polymerized). In the tubular reactors, the catalyst is inside a multiplicity of tubes which are cooled by a steam-water condensate jacket. Thus, the heat of reaction is utilized to generate high pressure steam. In the chamber process, the catalyst is held in several beds in a drum-type reactor with feed or recycled product introduced as a quench between the individual beds. 

The maximum or minimum temperature attainable in a vessel can be limited by properly designed jacket heating systems. If steam heating is used, maximum temperatures can be limited by controlling steam pressure. A steam desuperheater may be needed to avoid excessive temperature of superheated steam from a pressure letdown station. 

The diverse types of plant in this category would be too numerous to list, but include steam-jacketed pans, steam calorifiers, steam heating and drying units and all types of air-pressure vessels. These are manufactured in a wide range of materials (e.g. stainless steel) and may then be lined with materials such as mbber or glass, depending on the needs of the process in which the vessel will be used. 

The common heater block shown in Fig. 19.23 can itself be subject to corrosion leading to different heat transfer conditions for different tubes, and in some later versions of the apparatus individual short heating jackets are used for each tube, which are heated with oil from either a steam-heated or electrically heated heat exchanger. This modification not only avoids corrosion problems but also obviates the necessity to machine a length of the outside of each tube to fit the semi-circular notches in the single heater block. The oil flow is adjusted to give an oil temperature of 95°C at each outlet. 

From this equation, the time t of heating from 7j to T2, may be calculated. The same analysis may be used if the steam condenses in a jacket of a reaction vessel. 

The epoxide and the nitrogen compound were mixed and stirred in a 250 1 reactor fitted for reflux and protected by a rupture disk. After addition of the catalyst, subsequent heating to the required temperature seems to have been effected by direct application of steam to the jacket, rather than the usual hot water. The too-rapid heating led to a violently exothermic reaction which ruptured the disk and stretched the lid clamping bolts. 

Emulsion tank The emulsion tank consists of a jacketed, agitated 50-gal glass-lined Pfaudler reactor with N2 pad and relief valve. Emulsion is heated in the vessel by applying steam to... 

In most jacketed reactors or steam-heated reboilers the volume occupied by the steam is quite small compared to the volumetric flow rate of the steam vapor. Therefore the dymamic response of the jacket is usually very fast, and simple algebraic mass and energy balances can often be used. Steam flow rate is set equal to condensate flow rate, which is calculated by iteratively solving the heat-transfer relationship (Q = UA AT) and the valve flow equation for the pressure in the jacket and the condensate flow rate. 

Figure 3.4. Diagram of a typical jacketed processing vessel. Such vessels are usually made from high grade stainless steel. By opening/closing the appropriate valves, steam or cold water can be circulated through the jacket. In this way, the vessel s contents can be heated or cooled, as appropriate. In addition, passage of steam through the jacket of the empty vessel will effectively sanitize its internal surfaces...

As a rule fusible mixtures are prepared in metallic kettles heated with steam or water jackets and fitted with stirrers, which are emptied either by tilting or through a valve placed in the bottom of the vessel. 

It must be borne in mind that generally aromatic nitro compounds are not highly sensitive to impact and friction, but become more sensitive at elevated temperatures as they melt (changes in the sensitiveness of TNT are discussed in Vol. I, p. 319). If, therefore, a mechanical device is used for the preparation of mixtures by melting, its construction should be such as to exclude any possibility of friction or impact. It is probably best to use a converter heated with steam or water jackets and fitted with a stirrer that can be lifted out by a special arrangement. After the stirrer has been removed, the contents are poured out by tilting the vessel. 

Carlisle (Ref 3) reported an expln occurred when its soln in acct was coned in a glass-lined steam jacketed vessel. The cause of this expln was not detd but examination of the subst showed that it was slightly flammable bur did not explode when unconfined. Therefore, on heating in a closed system a pressure release valve should be provided... 

If steam heat is to be used, what pressure will be used in the Jacket . 

Water is heated by passing it through a steam-heated kettle (Fig. 7.78) at a mass flowrate w. The inlet and outlet temperatures of the water are 9, and 9 respectively. Steam condenses in the jacket of the kettle at a temperature 0, and a pressure f. It is intended to control the temperature of the water by placing a temperature sensor in the water in the kettle and using this measurement to manipulate the flow of steam to the kettle jacket. In order to tune the controller it is necessary to derive the transfer functions relating 0o to 0j, 0, and w. 

All the animation reactions are conducted in a 100-gal stainless steel reactor heated with 75 psi steam to the jacket. The reactor is fitted with an ammonia inlet, a vent tube for azeo-troping w from the system and a thermowell The TCTNB is first dissolved in toluene in a feed vessel and passed thru a 1.5 pm in-line filter during transfer to the reactor. The soln is then heated to 140° and the w azeotroped from the system. The ullage is then backfilled with ammonia and the temp brought to 150°. The... 

---