Series temperature control

A third principle can be realized with two possibilities - the counter-flow principle. In this case, the channels are arranged so that cold and hot channel sections run past each other, and temperature differences can almost be canceled out. In many cases, this principle is used for the flat series temperature control (e.g., as a spiral) wherein the spiral is guided from the outside to inside and again from the inside to the outside. The average value between warm and cold spiral section is always the same. 

FIGURE 2.84 Flat series temperature control using transverse bore holes and sealing plugs [4]... 

These enable temperature control with built-in exchangers between the beds or with pumparound exchangers. Converters for ammonia, 80.3, cumene, and other processes may employ as many as five or six beds in series. The Sohio process for vapor-phase oxidation of propylene to acrylic acid uses hvo beds of bismuth molybdate at 20 to 30 atm (294 to 441 psi) and 290 to 400°C (554 to 752°F). Oxidation of ethylene to ethylene oxide also is done in two stages with supported... 

Figure 4-8 shows a continuous reactor used for bubbling gaseous reactants through a liquid catalyst. This reactor allows for close temperature control. The fixed-bed (packed-bed) reactor is a tubular reactor that is packed with solid catalyst particles. The catalyst of the reactor may be placed in one or more fixed beds (i.e., layers across the reactor) or may be distributed in a series of parallel long tubes. The latter type of fixed-bed reactor is widely used in industry (e.g., ammonia synthesis) and offers several advantages over other forms of fixed beds. 

The chapter by White et al. proposes a different approach to metha-nator temperature control. Here the temperature rise is controlled by limiting the amount of reaction in each stage, and that is done by introducing steam (a product of the reaction). High initial temperatures are followed by successively lower temperatures entering each reactor in series. This is a second-generation methanation approach which may follow closely on the first-generation approaches typified by the previous three papers. 

Operability. All four series of experiments prove that HGR metha-nation is a usable and operable system. With a total gas recycle ratio of about 10 1 and with CO concentrations in the mixed feed entering the catalyst bed as high as 4.3% (wet basis), temperature control was excellent and no hot spots developed. It appears likely that lower recycle... 

Nickel catalysts were used in most of the methanation catalytic studies they have a rather wide range of operating temperatures, approximately 260°-538°C. Operation of the catalytic reactors at 482°-538°C will ultimately result in carbon deposition and rapid deactivation of the catalysts (10). Reactions below 260°C will usually result in formation of nickel carbonyl and also in rapid deactivation of the catalysts. The best operating range for most fixed-bed nickel catalysts is 288°-482 °C. Several schemes have been proposed to limit the maximum temperature in adiabatic catalytic reactors to 482°C, and IGT has developed a cold-gas recycle process that utilizes a series of fixed-bed adiabatic catalytic reactors to maintain this temperature control. 

The continuous polystyrene process which was commercialized successfully in 1952 (2) is illustrated schematically in Fig. 16. It is characterized by three vertical elongated reactors in series, the contents of which are gently agitated by slowly revolving rods mounted on an axial shaft. Temperature control is provided by horizontal banks of cooling tubes between adjacent agitator rods. Such a reactor, called a "stratifier-... 

Application of Time to Temperature Control of Semi-Batch Reactors... 

The catalytic reforming of CH4 by CO2 was carried out in a conventional fixed bed reactor system. Flow rates of reactants were controlled by mass flow controllers [Bronkhorst HI-TEC Co.]. The reactor, with an inner diameter of 0.007 m, was heated in an electric furnace. The reaction temperatoe was controlled by a PID temperature controller and was monitored by a separated thermocouple placed in the catalyst bed. The effluent gases were analyzed by an online GC [Hewlett Packard Co., HP-6890 Series II] equipped with a thermal conductivity detector (TCD) and carbosphere column (0.0032 m O.D. and 2.5 m length, 80/100 meshes), and identified by a GC/MS [Hewlett Packard Co., 5890/5971] equipped with an HP-1 capillary column (0.0002 m O.D. and 50 m length). 

The high pressure continuous reactor consists of five Kenics type in-line static mixers, that were connected in series [3]. Each reactor unit has 27 Kenics elements and dimensions of 19 cm tube length and 3.3 mm inner diameter. Acetonylacetone and 1 % NaOH aqueous solution were pumped into the in-line static mixer reactor using two independent HPLC pumps. The in-line static mixer reactors were immersed in a constant temperature controlled oil bath at 200 °C so that the reaction mixture was heated to the reaction temperature. When the reaction was completed, the fluid was cooled down rapidly in a constant temperature cold bath at 0 °C. At the end of the cooling line, a backpressure regulator was placed to allow experiments to be run at 34 bar. 

Temperature-Controlled Residuiun Oil Supercritical Extraction (ROSE) The Kerr-McCee ROSE process has been used worldwide for over two decades to remove asphaltenes from oil. The extraction step uses a hquid solvent that is recovered at supercritical conditions to save energy as shown in Fig. 20-21. The residuum is contacted with butane or pentane to precipitate the heavy asphaltene fraction. The extract is then passed through a series of heaters, where it goes from the liquid state to a lower-density SCF state. Because the entire process is carried out at conditions near the critical point, a relatively small temperature change is required to produce a fairly large density change. After the light oils have been removed, the solvent is cooled back to the liquid state and recycled. 

Coleman and Sivy also used an infrared transmission cell to undertake degradation studies under reduced pressure on a series of poly(acrylonitrile) (ACN) copolymers [30-33]. Thin films prepared from a polymer were mounted in the specially designed temperature-controlled cell mounted within the infrared spectrometer. The comparative studies were made on ACN copolymers containing vinyl acetate [30,32], methacrylic acid [30,31] and acrylamide [30,33]. The species monitored was the production of the cyclised pyridone structure. This was characterised in part by loss of C=N stretch (vC = N) intensity at 2,240 cm-1 accompanied by the appearance and increase in intensity of a doublet at 1,610/1,580 cm-1. 

The electrolyte used in the lithium cell studies was typically 1,2M LiPF6 in ethylene carbonate (EC) propylene carbonate (PC) methyl ethyl carbonate (MEC) in a 3 3 4 mixture. The cells were cycled at room temperature using Maccor Series 4000 control unit in a galvanostatic mode under a constant current density of 0.1 to 1 mA/cm2. 

Similar to its predecessors of the Emrys series, the operation limits for the Initiator system are 60-250 °C at a maximum pressure of 20 bar. Temperature control is achieved in the same way by means of an IR sensor perpendicular to the sample position. Thus, the temperature is measured on the outer surface of the reaction vessels, and no internal temperature measurement is available. Pressure measurement is accomplished by a non-invasive sensor integrated into the cavity lid, which measures the deformation of the Teflon seal of the vessels. Efficient cooling is accomplished by means of a pressurized air supply at a rate of approximately 60 L min-1, which enables cooling from 250 °C to 40 °C within one minute. 

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