Equation (10a) is somewhat inconvenient first, because we prefer to use pressure rather than volume as our independent variable, and second, because little is known about third virial coefficients It is therefore more practical to substitute  [c.28]

In this chapter we present efficient calculation procedures for single-stage equilibrium separations subroutines implementing these procedures are given in Appendices F and G. While we recognize the great importance of multistage separations, it must be realized that the efficient computation of such processes requires very careful resolution of the large number of simultaneous equilibrium stages involved in a countercurrent cascade. The dominant consideration in such multistage computation procedures is usually the technique used to achieve this simultaneous solution rather than the equilibrium treatment of the stages themselves. (Goldstein and Stanfield, 1970 Holland,  [c.110]

Large values of the uncertainty are assigned to the generated points, because the primary purpose of the generated points is not to have them fit accurately, but rather to maintain a reasonable slope of the function in the range outside the experimental points.  [c.140]

RATER ACETONE VL 1 2 309-339 - 1 17,35 572.52 23. 25 OTHMER,1945  [c.201]

The preference is for a process based on ethylene rather than the more expensive acetylene and chlorine rather than the more expensive hydrogen chloride. Electrolytic cells are a much more convenient and cheaper source of chlorine than hydrogen chloride. In addition, we prefer to produce no byproducts.  [c.17]

Multiple reactions in parallel producing byproducts. Rather than a single reaction, a system may involve secondary reactions producing (additional) byproducts in parallel with the primary reaction. Multiple reactions in parallel are of the tj ie  [c.19]

Multiple reactions in series producing byproducts. Rather than  [c.19]

In describing reactor performance, selectivity is usually a more meaningful parameter than reactor yield. Reactor yield is based on the reactant fed to the reactor rather than on that which is consumed. Clearly, part of the reactant fed might be material that has been recycled rather than fresh feed. Because of this, reactor yield takes no account of the ability to separate and recycle unconverted raw materials. Reactor yield is only a meaningful parameter when it is not possible for one reason or another to recycle unconverted raw material to the reactor inlet. By constrast, the yield of the overall process is an extremely important parameter when describing the performance of the overall plant, as will be discussed later.  [c.25]

For all reversible secondary reactions, deliberately feeding BYPRODUCT to the reactor inhibits its formation at the source by shifting the equihbrium of the secondary reaction. This is achieved in practice by separating and recycling BYPRODUCT rather than separating and disposing of it directly.  [c.38]

Multiple reactions. The arguments presented for minimizing reactor volume for single reactions can be used for the primary reaction when dealing with multiple reactions. However, the goal at this stage of the design, when dealing with multiple reactions, is to maximize selectivity rather than to minimize volume for a given conversion.  [c.41]

As well as depending on catalyst porosity, the reaction rate is some function of the reactant concentrations, temperature, and pressure. However, this function may not be as simple as in the case of uncatalyzed reactions. Before a reaction can take place, the reactants must diffuse through the pores to the solid surface. This results in a situation where either reaction or diffusion can be the rate-limiting process. Alternatively, it may be that reaction speed and diffusion have an almost equal effect. If reaction is rate limiting, as tends to occur in a lower temperature range, the effects of concentration and temperature are those typical of chemical reaction. On the other hand, if diffusion is rate limiting, as tends to occur in a higher temperature range, the effects of concentration and temperature are those characteristic of diffusion. In the transitional region, where both reaction and diffusion affect the overall rate, the effects of temperature and concentration are often rather complex.  [c.47]

Solution The byproduct reactions to avoid are all series in nature. This suggests that we should not use a continuous well-mixed reactor but rather use either a batch or plug-flow reactor.  [c.52]

Other designs of kilns use static shells rather than rotating shells and rely on mechanical rakes to move solid material through the reactor.  [c.60]

The decisions made in the reactor design are often the most important in the whole flowsheet. The design of the reactor usually interacts strongly with the rest of the flowsheet. Hence a return to the decisions made for the reactor must be made when the process design has progressed further and we have fully understood the consequences of those decisions. For the detailed sizing of the reactor, the reader is referred to the many excellent texts on reactor design.  [c.64]

If the mixture to be separated is homogeneous, a separation can only be performed by the addition or creation of another phase within the system. For example, if a gaseous mixture is leaving the reactor, another phase could be created by partial condensation. The vapor resulting from the partial condensation will be rich in the more volatile components and the liquid will be rich in the less volatile components, achieving a separation. Alternatively, rather than creating another phase, one can be added to the gaseous mixture, such as a solvent which would preferentially dissolve one or more of the components from the mixture. Further separation is required to separate the solvent from the process materials allowing recycle of the solvent, etc. A number of physical properties can be exploited to achieve the separation of homogeneous mixtures.If a heterogeneous or multiphase mixture leaves the reactor, then separation can be done physically by exploiting differences in density between the phases.  [c.67]

The separation of suspended solid particles from a liquid by gravity settling into a clear fiuid and a slurry of higher solids content is called sedimentation. Figure 3.2 shows a sedimentation device known as a thickener, the prime function of which is to produce a more concentrated slurry. The feed slurry in Fig. 3.2 is fed at the center of the tank below the surface of the liquid. Clear liquid overflows from the top edge of the tank. A slowly revolving rake removes the thickened slurry or sludge and serves to scrape the sludge toward the center of the base for removal. It is common in such operations to add a flocculating agent to the mixture to assist the settling process. This agent has the effect of neutralizing electric charges on the particles that cause them to repel each other and remain dispersed. The effect is to form aggregates or floes which, because they are larger in size, settle more rapidly. When the prime function of the sedimentation is to remove solids from a liquid rather than to produce a more concentrated solid-liquid mixture, the device is known as a clarifier. Clarifiers are often similar in design to thickeners.  [c.69]

Rather than use a cloth, a granular medium consisting of layers of particulate solids on a support grid can be used. Downward fiow of the mixture causes the solid particles to be captured within the medium. Such deep-bed filters are used to remove small quantities of solids from large quantities of liquids. To release the solid particles captured within the bed, the flow is periodically reversed, causing the bed to expand and release the particles which have been captured. Around 3 percent of the throughput is needed for this backwashing.  [c.74]

When separating azeotropic mixtures, if possible, changes in the azeotropic composition with pressure should be exploited rather than using an extraneous mass-separating agent. When using an extraneous mass-separating agent, there are inevitably losses from the process. Even if these losses are not significant in terms of the cost of the material, they create environmental problems somewhere later in the design. As discussed in detail in Chap. 10, the best way to solve effluent problems is to deal with them at the source. The best way to solve the effluent problems caused by loss of the extraneous mass-separating agent is to eliminate it from the design. However, clearly in many instances practical difficulties and excessive cost might force its use. Occasionally, a component that already exists in the process can be used as the entrainer or solvent, thus avoiding the introduction of extraneous materials for azeotropic and extractive distillation.  [c.83]

Because we require a pure product, a separator is needed. The unreacted FEED is usually too valuable to be disposed of and is therefore recycled to the reactor inlet via a pump or compressor (see Fig. 4.16). In addition, disposal of unreacted FEED rather than recycling creates an environmental problem.  [c.96]

Where possible, introducing extraneous materials into the process should be avoided, and a material already present in the process should be used. Figure 4.6h illustrates use of the product as the heat carrier. This simplifies the recycle structure of the flowsheet and removes the need for one of the separators (see Fig. 4.66). Use of the product as a heat carrier is obviously restricted to situations where the product does not undergo secondary reactions to unwanted byproducts. Note that the unconverted feed which is recycled also acts as a heat carrier itself. Thus, rather than relying on recycled product to limit the temperature rise (or fall), simply opt for a low conversion, a high recycle of feed, and a resulting small temperature change.  [c.101]

In other words, the process must convert at least 53 percent of the decane which reacts to monochlorodecane rather than to dichlorodecane for the process to be economic. This figure assumes selling the hydrogen chloride to a neighboring process. If this is not the case, there is no value associated with the hydrogen chloride. Assuming that there are no treatment and disposal costs for the now waste hydrogen chloride, the minimum economic potential is given by  [c.105]

Rather than send the vapor to one of the separation units described above, a purge can be used. This removes the need for a separator but incurs raw material losses. Not only can these material losses be expensive, but they also can create environmental problems. However, another option is to use a combination of a purge with a separator.  [c.109]

The reader might wish to check that if the temperature of the phase split is increased or its pressure decreased, the separation between hydrogen, methane, and the other components becomes worse.  [c.114]

Given the choice of a batch rather than continuous process, does this need a different approach to the synthesis of the reaction and separation and recycle system In fact, a different approach is not needed. We start by assuming the process to be continuous and then, if choosing to use batch operation, replace continuous steps by batch steps. It is simpler to start with continuous process operation  [c.117]

Rather than relying on heuristics which can be ambiguous or in conflict, a parameter would be preferred that can measure quantitatively the relative performance of different sequences. The vapor flow rate up the column is a good measure of both capital and operating costs. There is clearly a relationship between the heat duty required to run the distillation and the vapor rate, since the latent heat relates these two parameters. However, there is also a link between vapor rate and capital cost, since a high vapor rate leads to a large-diameter column. The high vapor rate also requires large reboilers and condensers. Thus vapor rate is a good measure of both capital and operating costs on individual columns. Consequently, sequences with a lower total vapor load would be preferred to those with a high total vapor load. But how is the total vapor load predicted  [c.135]

This result is important, since in practice we should not focus exclusively on the single sequence with the lowest overall cost. Rather, because of the uncertainties in the calculations and the fact that other factors need to be considered in a more detailed evaluation, the best few sequences should be evaluated in more detail. Thus there is no need to solve the separation sequence and heat integration problems simultaneously. Rather, decouple the two problems and tackle them separately, simplifying considerably the overall task. It must be emphasized strongly that the decoupling depends on the absence of significant constraints limiting the heat integration potential within the distillation sequence. For example, there may be limitations on the pressure of some of the columns due to product decomposition, etc. that limit the heat integration potential. In these  [c.143]

It is thus recommended that in a first pass through a design, thermal coupling should not be considered. Rather, simple columns should be used until a first overall design has been established. Only when the full heat-integration context has been understood should thermal coupling be considered.  [c.155]

Using targets rather than design for the outer layers allows many design alternatives to be screened quickly and conveniently. Screening many design alternatives by complete designs is usually simply not practical in terms of the time and effort required. Using targets to suggest design changes works inward to the center of ttie onion and evolves the design for the inner layers. First, consider Hie details of how to set energy targets. Capital cost targets are considered in the  [c.159]

Find a way to overcome the constraint while still maintaining the areas. This is often possible by using indirect heat transfer between the two areas. The simplest option is via the existing utility system. For example, rather than have a direct match between two streams, one can perhaps generate steam to be fed into the steam mains and the other use steam from the same mains. The utility system then acts as a buffer between the two areas. Another possibility might be to use a heat transfer medium such as a hot oil which circulates between the two streams being matched. To maintain operational independence, a standby heater and cooler supplied by utilities is needed in the hot oil circuit such that if either area is not operational, utilities could substitute heat recovery for short periods.  [c.184]

In Sec. 4.4 the possibility of using batch rather than continuous operations in the flowsheet was discussed. At that time, our only interest was the recycle structure of the flowsheet. There the approach was first to synthesize a flowsheet based on continuous  [c.248]

Here we shall restrict consideration to safety and health considerations that can be built in while the design is developing rather than the detailed hazard and operability studies that take place in the later stages of design. The three major hazards in process plants are fire, explosion, and toxic release.  [c.255]

Physical energy. Physical energy may be pressure energy in gases, thermal energy, strain energy in metal, or electrical energy. An example of an explosion caused by release of physical energy would be fracture of a vessel containing high-pressure gas. Thermal energy is generally important in creating the conditions for explosions rather than as a source of energy for the explosion itself. In particular, as already mentioned, superheat in a liquid under pressure causes flashing of the liquid if it is accidentally released to the atmosphere.  [c.257]

Vapor Treatment. The vapors from the tank space can be sent to a treatment system (condenser, absorption, etc.) before venting. The system shown in Fig. 9.1 uses a vacuum-pressure relief valve which allows air in from the atmosphere when the liquid level falls (Fig. 9.1a) but forces the vapor through a treatment system when the tank is filled (Fig. 9.16). If inert gas blanketing is required, because of the flammable nature of the material, then a similar system can be adopted which draws inert gas rather than air when the liquid level falls.  [c.260]

So far the emphasis has been on substituting hazardous materials or using less, i.e., intensification. Let us now consider use of hazardous materials under less hazardous conditions, i.e. at less extreme temperatures or pressures or as a vapor rather than superheated liquid or diluted, in other words, attenuation.  [c.267]

Design continuous processes for flexible operation, e.g., high turndown rate rather than shutdown.  [c.290]

Waste from cooling systems. Cooling water systems also give rise to wastewater generation. Most cooling water systems recirculate water rather than using once through arrangements. Water is lost from recirculating systems in the cooling tower mainly through evaporation but also, to a much smaller extent, through drift (wind carrying away water droplets). This loss is made up by raw water which contains solids. The evaporative losses from the cooling tower cause these solids to build up. The buildup of solids is prevented by a purge of water from the system, i.e., cooling tower blowdown. Cooling tower blowdown is the source of the largest volume of wastewater on many sites.  [c.294]

This is the order in which we should look to solve the problem of SO,c emissions. We should try to prevent creation of the waste, since treating the waste tends only to move the problem rather than solve it.  [c.306]

The capital cost of most aqueous waste treatment operations is proportional to the total flow of wastewater, and the operating cost increases with decreasing concentration for a given mass of contaminant to be removed. Thus, if two streams require different treatment operations, it makes no sense to mix them and treat both streams in both treatment operations. This will increase both capital and operating costs. Rather, the streams should be segregated and treated separately in a distributed effluent treatment system. Indeed, effective primary treatment might mean that some streams do not need biological treatment at all.  [c.310]

In attached growth film) methods, as with aerobic digestion, the microorganisms can be encouraged to grow attached to a support medium such as plastic packing or sand. In anaerobic digestion, the bed is usually fluidized rather than a fixed-bed  [c.316]

Multiple reactions in parallel producing byproducts. Raw materials costs usually will dominate the economics of the process. Because of this, when dealing with multiple reactions, whether parallel, series, or mixed, the goal is usually to minimize byproduct formation (maximize selectivity) for a given reactor conversion. Choice of reactor conditions should exploit diflTerences between the kinetics and equilibrium effects in the primary and secondary reactions to favor the formation of the desired product rather than the byproduct, i.e., improve selectivity. Making an initial guess for conversion is more difficult than with single reactions, since the factors that affect conversion also can have a significant effect on selectivity.  [c.26]

Choosing to use a continuous rather than a batch reactor, plug-flow behavior can be approached using a series of continuous well-mixed reactors. This again sdlows concentrated sulfuric acid to be added as the reaction progresses, in a similar way as suggested for some parallel systems in Fig. 2.2. Breaking the reactor down into a series of well-mixed reactors also allows good temperature control, s we shall discuss later.  [c.52]

Whatever the method used to screen possible sequences, it is important not to give exclusive attention to the one that appears to have the lowest vapor load or lowest total cost. There is often little to choose in this respect between the best few sequences, particularly when the number of possible sequences is large. Other considerations such as heat integration, safety, and so on also might have an important bearing on the final decision. Thus the screening of sequences should focus on the best few sequences rather th2in exclusively on the single best sequence.  [c.142]

The output from the turbine might be superheated or partially condensed, as is the case in Fig. 6.32. If the exhaust steam is to be used for process heating, ideally it should be close to saturated conditions. If the exhaust steam is significantly superheated, it can be desuperheated by direct injection of boiler feedwater, which vaporizes and cools the steam. However, if saturated steam is fed to a steam main, with significant potential for heat losses from the main, then it is desirable to retain some superheat rather than desuperheat the steam to saturated conditions. If saturated steam is fed to the main, then heat losses will cause excessive condensation in the main, which is not desirable. On the other hand, if the exhaust steam from the turbine is partially condensed, the condensate is separated and the steam used for heating.  [c.195]

See pages that mention the term RADAR : [c.15]    [c.201]    [c.201]    [c.11]    [c.39]    [c.131]    [c.192]    [c.271]   
Modern spectroscopy (2004) -- [ c.379 ]