Stream specifications

A stream-specific cost-weighting factor 4)j to apply to the h value of a special stream j can now he defined. This is the ratio of weighted to actual stream h values ... 

The outside stream specific heat Cp and mass flow rate Gt falls in temperature from Tn It) Ti2-... 

The inside stream specific heat Cp2 and mass flow rate G2 rises in temperature from T21 to T22. 

When carrying out the problem table algorithm, the temperatures were shifted according to ATmin/2 being added to the cold streams and subtracted from the hot streams. This value of ATmin/2 can be considered to be a contribution to the overall A Tmin between the hot and the cold streams. Rather than making the A Tmin contribution equal for all streams, it could be made stream-specific ... 

The pinch design method, as discussed so far, has assumed the same A Tmin applied between all stream matches. In Chapter 16, it was discussed how the basic targeting methods for the composite curves and the problem table algorithm can be modified to allow stream-specific values of A Tmin. The example was quoted in which liquid streams were required to have a A Tmin contribution of 5°C and gas streams a ATmin contribution of 10°C. For liquid-liquid matches, this would lead to a ATmin = 10°C. For gas-gas matches, this would lead to a ATmin = 20°C. For liquid-gas matches, it will lead to a ATmin = 15°C 2. Modifying the problem table and the composite curves to account for these stream-specific values of ATmin is straightforward. But how is the pinch design method modified to take account of such A Tmin contributions Figure 18.9 illustrates the approach. Suppose the interval pinch temperature from the problem table is 120°C. This would correspond with hot stream pinch temperatures of 125°C and 130°C for hot streams with ATmin contributions of 5°C and 10°C respectively. For... 

Figure 18.9 The design grid for a problem stream-specific with A Tmm contributions.

Throughout the preceding discussion, simplified expressions of stream-specific enthalpy as a function of temperature are used. They have to be updated during process operation to consider changes in steady-state compositions. 

Gosling of UOP LLC patented the use of Raman spectroscopy to control a solid catalyst alkylation process.54 Based on the measured composition of the stream, specific process parameters are adjusted to bring the composition back to a targeted value. Multiple probes are placed in the process, for example, near a feed stock inlet, in the reaction zone, or after the reactor. In the process discussed, the catalyst can be deactivated faster than an on-line GC can produce a reading. This reason, coupled with obtaining greater process efficiency, is strong motivation for a fast on-line system like Raman. 

The solution to the problem is obtained by solving mass and energy balances to yield the quantity and state (i.e., composition, temperature, pressure) of all the streams and the utility requirements. Additional parameters for the process equipment, sufficient so that stream specifications are met and the cost of the equipment can be estimated, are calculated. The cost of equipment, raw materials, and utilities is estimated and an economic analysis is carried out. Methods of cost estimation and economic analysis are presented later in this text. This entire procedure may be repeated many times to examine modifications of the process flow sheet or to find optimal values of key process variables. Computer software can greatly simplify these repetitive calculations for the engineer. But even without the need for repetition, the software may simplify the calculations and provide detail and accuracy that would have been impossible otherwise. 

Internal energy of a system ill), rate of transport of internal energy by a process stream ((/), specific internal energy (U), all relative to a specified reference state. 

Volume (V) of a fluid or process unit, volumetric flow rate (V or fi) of a process stream, specific volume (V) of a process material. 

Hetal Contaminants in the Environment. From the perspective of environmental remediation, the focus of separation science should be on the metals currently being regulated from the standpoint of groundwater protection. This is not a hard and fast rule, as there are a number of situations (e.g., specific spills, waste-stream-specific toxins, etc.) where the focus will be on the removal of a specific hazardous metal compound or substance for which standards have not been set. For example, there is currently much emphasis within the DOE on uranium contamination at the Fernald Site in Ohio. 

Specifications 1 and 2 characterize the two product streams. Specifications 3 and 4 are required for operational feasibility (i.e., we do not want... 

When the tear stream is determined automatically by the process simulator, it is possible to override it. For example, ASPEN PLUS selects stream S2, but it can be replaced with stream S6. To do so, select Convergence from the Data pulldown menu. Then select Tern, which produces the Tear Streams Specifications form. Enter S6 as the tear stream. Other simulators permit the override in a similar manner. 

In addition to the physical and chemical sensors, there are a wide range of analyzers that are commonly used for analyzing chemical substances and/or other chemical characteristics in process streams. Specific examples of these analyzers are described below. 

Anionic dyes can be removed from textile effluent streams at acidic pH with chitosan through protonated amine complexation with anionic dye sites. Phenols are common waste products in paper processing. Application of mushroom enzyme tyrosinase to the stream specifically converts phenols into quinones, which can subsequently be absorbed by chitosan. Toxic polychlorinated hiphenols (PCBs), commonly used in plastic processing and lubricants, are a significant source of water contamination. Although the nature of the interaction is not currently known, chitosan treatment shows potential in lowering PCB concentrations. 

Entitlement control messi e (ECM) Entitlement control messages are private conditional access information that specify control words and possibly other stream-specific, scrambling, and/or control parameters. 

A quick check of the pump results shows that the pump causes a temperature rise that will cause poor performance in the absorber, which requires low temperatures. Therefore, add a Cooler block with a specified outlet temperature for the pumped, lean solvent of 10°C (enter this into the stream specifically). Not only will this provide better column performance, but without it, the steady-state solvent feed temperature will actually be much higher (about 50°C) once the recycle loop has been closed. 

In this chapter, you will learn how to analyze the reasons why the specific tenperatures, pressures, and compositions selected for inportant streams and unit operations have been chosen. Stream specifications and process conditions are influenced by physical processes as well as economic considerations and are not chosen arbitrarily. The conditions used in a process most often represent an economic conpromise between process performance and the capital and operating costs of the process equipment. Final selection of operating conditions should not be made prior to the analysis of the process economics. In this chapter, we concentrate on analyzing process conditions that require special consideration. As an exanple, we do not address why a reactor is run at 600°C instead of 580°C, but rather concentrate on the reasons why the reactor is not run at a much lower tenperature, for exanple, 200°C. This type of analysis leads us to question how process conditions are chosen and makes us consider the consequences of changing these conditions. 

Assume first that we are dealing with absorption/strip-ping from a dilute gas stream specifically, we assume constant flow rates of phases 1 (= g) and 2 (= t] along the length of the device and constant temperature and pressure of operation. The equation for the operating line (8.1.24) becomes equation (8.1.25) under the following conditions ... 

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