Gas temperature control

The chapter by Haynes et al. describes the pilot work using Raney nickel catalysts with gas recycle for reactor temperature control. Gas recycle provides dilution of the carbon oxides in the feed gas to the methanator, hence simulating methanation of dilute CO-containing gases which under adiabatic conditions gives a permissible temperature rise. This and the next two papers basically treat this approach, the hallmark of first-generation methanation processes. 

In order to permit meaningful measurements which could be related to particular reaction conditions, the oxidations were carried out in the apparatus shown in Figures 1 and 2. This gas-tight, closed circuit installation allowed pressure and temperature control, gas monitoring, and periodic withdrawals of small coal samples while reaction proceeded. The total free volume of the apparatus amounted to some 2200 cc. 

A) Converter layout a) Catalyst b) Heat exchanger c) Cooling tubes d) Main gas inlet e) Vessel wall cooling gas inlet f) Temperature control gas (cold-shot) inlet g) Gas exit... 

The experiments were carried out in a semi-batch stirred reactor with continuous oxygen feed. The reactor is a one liter Pyrex flask with flattened bottom and baffles which is fitted with five standard 24/40 necks to accomodate the gas inlet, gas vent, sampling tube, and pH electrode. The reactor is immersed in a standard water bath for temperature control. Gas is fed at a flow rate of 3.0 + 0.1 1/min through a rotameter. The solution is stirred at 1620 rpm. 

Fluidization of the uncoated support material by means of a temperature-controlled gas flow, such as air, nitrogen, or argon, is followed by addition of a solution of catalyst and IL, sprayed onto the material through a nozzle shown in detail in Figure 4.7(b). The molecular solvent evaporates rapidly because of the gas flow, resulting in a good dispersion of the ionic catalyst solution onto the support... 

Figure 6.1.13 Multibed NH3 reactor with indirect cooling (3) cooling section, (5) inlet of temperature control gas (cold-shot), (6) gas exit for other notation see Figure 6.1.12 (adapted from Appl, 1999).

Both voltammetric and chronoamperometric measurements were performed using Autolab general pnupose electrochemical system (Ecochemie, Netherland). A lab-constructed singlecell system with temperature control, gas flow rate and paessure control, and liquid flow rate and pressure control constructed was used for the measurements of fuel cell p>erformance. 

Culture system Mixing Light utilization Temperature control Gas transfer Monoculture Sterility Scale-up... 

A number of potential sources of error must be taken into account. In the volumetric method the following items need attention (a) constancy of the level of liquid nitrogen (b) depth of immersion of the sample bulb ( S cm) (c) temperature of sample (monitoring with vapour pressure thermometer close to sample bulb) (d) purity of adsorptive (preferably 99-9 per cent) (e) temperature of gas volumes (doser, dead space), controlled to 01 C. 

Control of sonochemical reactions is subject to the same limitation that any thermal process has the Boltzmann energy distribution means that the energy per individual molecule wiU vary widely. One does have easy control, however, over the energetics of cavitation through the parameters of acoustic intensity, temperature, ambient gas, and solvent choice. The thermal conductivity of the ambient gas (eg, a variable He/Ar atmosphere) and the overaU solvent vapor pressure provide easy methods for the experimental control of the peak temperatures generated during the cavitational coUapse. 

The catalytic vapor-phase oxidation of propylene is generally carried out in a fixed-bed multitube reactor at near atmospheric pressures and elevated temperatures (ca 350°C) molten salt is used for temperature control. Air is commonly used as the oxygen source and steam is added to suppress the formation of flammable gas mixtures. Operation can be single pass or a recycle stream may be employed. Recent interest has focused on improving process efficiency and minimizing process wastes by defining process improvements that use recycle of process gas streams and/or use of new reaction diluents (20-24). 

Chlorine Trifluoride. Chlorine trifluoride is produced commercially by the continuous gas-phase reaction of fluorine and chlorine ia a nickel reactor at ca 290°C. The ratio of fluorine to chlorine is maintained slightly in excess of 3 1 to promote conversion of the chlorine monofluoride to chlorine trifluoride. Sufficient time ia the reactor must be provided to maintain high conversions to chlorine trifluoride. Temperature control is also critical because the equiHbrium shift of chlorine trifluoride to chlorine monofluoride and fluorine is significant at elevated temperatures. 

The hot gases from the combustor, temperature controlled to 980°C by excess air, are expanded through the gas turbine, driving the air compressor and generating electricity. Sensible heat in the gas turbine exhaust is recovered in a waste heat boiler by generating steam for additional electrical power production. 

Catalytic Incinerators. Catalytic incinerators, often used to remove hydrocarbons from exhaust gas streams, are more compact than direct-flame incinerators, operate at lower temperatures, often require Htfle fuel, and produce Httle or no NO from atmospheric fixation. However, the catalytic bed must be preheated and carefliUy temperature controlled. Thus these are generally unsuited to intermittent and highly variable gas flows. 

As the width and thickness of IC layers and patterns continue to shrink into the submicrometer range, Si02 layers need to be fabricated of 5—20 nm thickness. These thin oxides have properties that are very sensitive to the substrate cleanliness and uniformity, gas purity, and temperature control. 

Schemes to control the outlet temperature of a process furnace by adjusting the fuel gas flow are shown in Figure 13. In the scheme without cascade control (Fig. 13a), if a disturbance has occurred in the fuel gas supply pressure, a disturbance occurs in the fuel gas flow rate, hence, in the energy transferred to the process fluid and eventually to the process fluid furnace outlet temperature. At that point, the outlet temperature controller senses the deviation from setpoint and adjusts the valve in the fuel gas line. In the meantime, other disturbances may have occurred in the fuel gas pressure, etc. In the cascade control strategy (Fig. 13b), when the fuel gas pressure is disturbed, it causes the fuel gas flow rate to be disturbed. The secondary controller, ie, the fuel gas flow controller, immediately senses the deviation and adjusts the valve in the fuel gas line to maintain the set fuel gas rate. If the fuel gas flow controller is well tuned, the furnace outlet temperature experiences only a small disturbance owing to a fuel gas supply pressure disturbance.

Fig. 13. Cascade control schemes, where TC = temperature controller FC = fuel gas flow controller and LC = liquid level controller, (a) Simple circuit having no cascade control (b) the same circuit employing cascade control and (c) and (d) Hquid level control circuits with and without cascade control,...

Catalyst Development. Traditional slurry polypropylene homopolymer processes suffered from formation of excessive amounts of low grade amorphous polymer and catalyst residues. Introduction of catalysts with up to 30-fold higher activity together with better temperature control have almost eliminated these problems (7). Although low reactor volume and available heat-transfer surfaces ultimately limit further productivity increases, these limitations are less restrictive with the introduction of more finely suspended metallocene catalysts and the emergence of industrial gas-phase fluid-bed polymerization processes. 

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