Drop minimum rule

Benchmarks for 2003 facilities. The benchmarks developed for new entrants were also used to calculate allocations to incumbent sites that began operation in 2003, but for which insufficient data were available to apply the drop minimum rule. However, allowances for these sites are not deducted from the new entrants reserve. Instead they are deducted from the residual sector allocations available to other incumbents, before the incumbent emissions are divided among sites for which sufficient historical data were available. 

The problem presented to the designer of a gas-absorption unit usually specifies the following quantities (1) gas flow rate (2) gas composition, at least with respect to the component or components to be sorbed (3) operating pressure and allowable pressure drop across the absorber (4) minimum degree of recoverv of one or more solutes and, possibly, (5) the solvent to be employed. Items 3, 4, and 5 may be subject to economic considerations and therefore are sometimes left up to the designer. For determining the number of variables that must be specified in order to fix a unique solution for the design of an absorber one can use the same phase-rule approach described in Sec. 13 for distillation systems. 

From the functional form of Eq. 12.5, it is easy to see that as distance between the molecules rjj becomes small, the potential becomes very repulsive due to the dominance of the first term (r 12 dependence). However, the repulsive term drops off very rapidly with distance, and the attractive term dominates at long distances. The interaction potential has a minimum at some intermediate distance, with a characteristic attractive well-depth. The parameter oij represents a net collision diameter, and etj determines the depth (strength) of the interaction. Methods for obtaining these parameters from experiment and other estimation techniques are discussed in Section 12.2.3. Combining rules to estimate the parameters interactions between unlike molecules are given in Section 12.2.4. 

Pressure drop. Good control requires a substantial pressure drop through the valve. For pumped systems, the drop through the valve should be at least 1/3 of the pressure drop in the system, with a minimum of IS psi. When the expected variation in flow is small, this rule can be relaxed. In long liquid transportation lines, for instance, a fully open control valve may absorb less than 1% of the system pressure drop. In systems with centrifugal pumps, the variation of head with capacity must be taken into account when sizing the valve. Example 7.2, for instance, illustrates how the valve drop may vary with flow in such a system. 

Although the rate of heat transfer to or from fluids is improved by increase of linear velocity, such improvements are limited by the economic balance between value of equipment saving and cost of pumping. A practical rule is that pressure drop in vacuum condensers be limited to 0.5-1. Opsi (25-50 Ton) or less, depending on the required upstream process pressure. In liquid service, pressure drops of 5-10 psi are employed as a minimum, and up to 15% or so of the upstream pressure. 

As shown by the equations in Section 12.1, column plate height is affected by many parameters, including flow velocity, particle diameter, packing nonuniformity, diffusivities, degree of retention, stationary phase structure, temperature, pressure drop, and pressure. Some of these parameters are interdependent, such as diffusivity and temperature also velocity and pressure drop. Finding a minimum with respect to all of these parameters is an extended task we shall not attempt here. However, we can readily uncover some simple rules for optimizing a few of the major parameters. First we choose flow velocity. 

There are no set rules or parameters for maximum allowable pressure drop. Rather, an acceptable pressure drop is related to the velocity required to effect the heat transfer. For liquids a minimum velocity of 1-.3 feet per second should be considered. For gases rho-V squared should be maintained around 4000. 

When chlorine is released to a scrubber, a liquid stream containing at least enough caustic to neutralize the gas must be available to meet it. It is the product of caustic flow rate and concentration that matters. If the flow rate drops too low, or if the concentration of the solution is depleted too much, there will be a release of chlorine to the atmosphere. As a rule of thumb, if the minimiun NaOH strength is taken to be 5%, the required rate of flow of scrubbing solution in tons per horn is equal to the production rate of chlorine in tons per day [85]. For concentrations other than 5% NaOH, the required flow rate is inversely proportional to the minimum strength. 

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