Gas composition control

Lead and sulphur are derived from the fuel and there is a complex equilibrium dependent upon temperatures and gas composition controlling the absorption/desorption of these poisons. In the case of lead, extended trials have demonstrated the feasibility (ref. 20) of successful operation of oxidation catalysts on leaded fuel. However, it has been noted that in the decade since introduction of lead-free fuel in the USA, residual lead levels have fallen dramatically. In that market, where leaded and unleaded fuels are both available, incidents of poisoning reflect contamination of distribution equipment or deliberate misfuelling (refs. 21,22). Sulphur may also be derived from lube oil but its impact in the sense of poisoning is low on PGM catalysts. Interaction with catalyst components can, however, influence secondary/unregulated emissions of... 

This chapter will begin with the three-way-conversion (TWC) catalyst, which simultaneously converts CO, hydrocarbons and nitrogen oxides. TWC catalysts are currently used on all gasoline-powered passenger cars made in the US, as well as in many other world markets. The three milestones cited will be ceria, ceria-zirconia and close-coupled palladium. The first two of these bear on the central theme of gas-composition control, without which three-way conversion cannot be realized. The third milestone allowed the catalyst to become active at a much earlier point in the test cycle, leading to a major reduction in the amount of hydrocarbon emissions. 

Name three pile conditions where gas composition control might prove useful. 

Chromatographic techniques, particularly gas phase chromatography, are used throughout all areas of the petroleum industry research centers, quality control laboratories and refining units. The applications covered are very diverse and include gas composition, search and analysis of contaminants, monitoring production units, feed and product analysis. We will show but a few examples in this section to give the reader an idea of the potential, and limits, of chromatographic techniques. 

Compositional control ia suspension systems can be achieved with a corrected batch process. A suspension process has been described where styrene monomer is continuously added until 75—85% conversion, and then the excess acrylonittile monomer is removed by stripping with an iaert gas... 

An important advancement in carburizing has been the development of diffusion models to calculate the carbon gradient as a function of time as the gas composition and temperature change (13). Such models can be coupled with computer control of the gas composition and temperature to produce desired carbon profiles. 

Sulphur Trioxide (SO2 -I- O2) Linear reaction rates are observed due to phase boundary control by adsorption of the reactant, SO3. Maximum rates of reaction occur at a SO2/O2 ratio of 2 1 where the SO3 partial pressure is also at a maximum. With increasing 02 S02 ratio the kinetics change from linear to parabolic and ultimately, of course, approach the behaviour of the Ni/NiO system. At constant gas composition and pressure, the reaction also reaches a maximum with increasing temperature due to the decreasing SO3 partial pressure with increasing temperature, so that NiS04 formation is no longer possible and the reaction rate falls. 

The schematic diagram of the experimental setup is shown in Fig. 2 and the experimental conditions are shown in Table 2. Each gas was controlled its flow rate by a mass flow controller and supplied to the module at a pressure sli tly higher than the atmospheric pressure. Absorbent solution was suppUed to the module by a circulation pump. A small amount of absorbent solution, which did not permeate the membrane, overflowed and then it was introduced to the upper part of the permeate side. Permeation and returning liquid fell down to the reservoir and it was recycled to the feed side. The dry gas through condenser was discharged from the vacuum pump, and its flow rate was measured by a digital soap-film flow meter. The gas composition was determined by a gas chromatograph (Yanaco, GC-2800, column Porapak Q for CO2 and (N2+O2) analysis, and molecular sieve 5A for N2 and O2 analysis). The performance of the module was calculated by the same procedure reported in our previous paper [1]. 

Catalytic activity for the selective oxidation of H2S was tested by a continuous flow reaction in a fixed-bed quartz tube reactor with 0.5 inch inside diameter. Gaseous H2S, O2, H2, CO, CO2 and N2 were used without further purification. Water vapor (H2O) was introduced by passing N2 through a saturator. Reaction test was conducted at a pressure of 101 kPa and in the temperature range of 150 to 300 °C on a 0.6 gram catalyst sample. Gas flow rates were controlled by a mass flow controller (Brooks, 5850 TR) and the gas compositions were analyzed by an on-line gas chromotograph equipped with a chromosil 310 coliunn and a thermal conductivity detector. 

The gas metering section is designed to deliver controlled gas flows of C3H6 (Praxair, 99.99%), 02 (Praxair, 99.998%) and He (Praxair, 99.999%) to the reactor system via Brooks 5850 mass flow controllers at a total flow rate 40 ml/min. and latm pressure. Feed gas compositions are C3H6 (40%), 02 (10%) and He (50%) for the steady state reaction. Prior to each experiment, the catalyst was reduced in pure flowing H2 at 34 ml/min for 2 hours at 400 °C. 

A particularly attractive potential of plasma based methods is the ability to vary, continuously or discretely, the nature of the material deposited by varying the plasma parameters (eg flow rates, gas composition, power input, substrate temperature etc). This, of course, applies to organic as well as inorganic materials ( 3). This aspect of interface control is not yet well developed but is an exciting prospect. 

This results eventually in a closed loop control allowing an adjustment of the primary air ratio and thus providing constantly low pollutant emissions regardless of the fuel gas composition and the heat load of the appliance. 

There is of course attenuation of the signal, as shown in Fig. 5, taken from Joyner and Roberts (28) The gas phase spectrum will also be obtained, but this usually can be separated easily from the signal of the solid. This sample cell arrangement thus permits the study of the stationary-state surface during catalysis and also its evolution in response to pulses and step functions in the gas composition. The temperature of the sample should be controlled so that the surface can be studied during temperature-programmed desorption and reaction. 

The performance of a reactor for a gas-solid reaction (A(g) + bB(s) -> products) is to be analyzed based on the following model solids in BMF, uniform gas composition, and no overhead loss of solid as a result of entrainment. Calculate the fractional conversion of B (fB) based on the following information and assumptions T = 800 K, pA = 2 bar the particles are cylindrical with a radius of 0.5 mm from a batch-reactor study, the time for 100% conversion of 2-mm particles is 40 min at 600 K and pA = 1 bar. Compare results for /b assuming (a) gas-film (mass-transfer) control (b) surface-reaction control and (c) ash-layer diffusion control. The solid flow rate is 1000 kg min-1, and the solid holdup (WB) in the reactor is 20,000 kg. Assume also that the SCM is valid, and the surface reaction is first-order with respect to A. 

C02. If rapid maximization of hydrocarbon gas recovery is the only consideration, the injected gas should be 100% N2. The commercial and storage compromise will be between these two cases. We expect that the optimum commercial application will involve injecting variable gas composition to control storage volumes and the amount of N2 in the produced gas stream. The range of the N2 content in the injected gas is likely to be between 25% and 75%. 

---