Reactors waste minimization

Smith R and Petela EA (1992) Waste Minimization in the Process Industries Part 2 Reactors, Chem Eng, Dec(509-510) 17. 

Lakshmanan A, Biegler LT. Reactor network targeting for waste minimization. In El-Halwagi M, Petrides D, eds. Pollution Prevention via Process and Product Modifications AIChE Symposium Series 90. New York AIChE 128, 1994. 

Civilian applications are numerous, but most funding of SCWO technology has stemmed from the military s need to find a safe and effective alternative to incineration of their wastes, as well as the need to clean up mixed wastes (radioactive and hazardous organic materials) at DOE weapons facilities. For better utilization of SCWO for its application to a wide range of waste types, a better fundamental understanding of reaction media, including reaction rates, reaction mechanisms, and phase behavior of multicomponent systems is required. Such an understanding would help optimize the process conditions to minimize reactor corrosion and salt... 

The last two items in the above list involve considerable R D and hence present a long-term strategy for waste minimization in reactors. These items should be looked into carefully at the early stage of process design. The first three can be attempted in existing processes. 

Lakshmanan, A., and Biegler, L. T. "Reactor Network Targeting for Waste Minimization. presented at National AIChE Meeting. Atlanta. GA (1994). 

Materials science Pharmaceuticals Reactor technology Robotics V. Waste minimization ... 

Waste minimization in processes can be approached in a hierarchical order similar to that adopted in process design, starting with reactors and working through to utiUty systems. Thus waste is progressively identified and minimized in... 

The once-through fuel cycle could be entirely appropriate for initiating market penetration of small reactors without on-site refuelling. On the other hand, successful market penetration may lead to a requirement to close the fuel cycle as the way to achieve efficient waste minimization and fuel utilization. 

GREENSPAN, E., Generation-IV reactors and nuclear waste minimization, (Proc. of the 14 Pacific Basin Nuclear Conference, pp 032, Honolulu, Hawaii, March 21-25, 2004). 

Lakshmanan, A. aiid Biegler, L, T. (1995). Reactor network targeting for waste minimization. AIChE Symp. Ser., 98(303), 128-138. 

Armed with the PFS and the questions for the various process options the team can then discuss the most appropriate way forward. For example considering question 2, production staff may comment that this particular plant only runs on the day shift, so a 10-hour reaction is not viable the chemical engineer may conclude that the problem is likely to be one of mass transfer, and other reactor design options such as a spinning disc reactor should be considered. The SHE advisor may comment that not only is solvent 1 volatile but it is also moderately harmful and would require specialist handling equipment, hence it is very important to find an alternative. As waste minimization starts at the reaction stage it is critical to study this area in particular detail. Questions that can be asked include ... 

Is the proposed reactor the most efficient, from an energy efficiency and waste minimization point of view ... 

The Generation IV GFR is the robust nuclear reactor design offering a broad range of potential apphcations—from electricity to process heat to waste minimization. 

The properties of the fuel salt used in these simulations are summarized in Table 7.2. The fuel salt considered in the simulations is a molten binary fluoride salt with 77.5 mol% of lithium fluoride the other 22.5 mol% is a mixture of heavy nuclei fluorides. This proportion, maintained throughout the reactor evolution, leads to a fast neutron spectrum in the core as shown in Fig. 7.2. Thus this MSFR system combines the generic assets of fast neutron reactors (extended resource utilization, waste minimization) and those associated with a liquid-fueled reactor. 

In Chap. 2 the objective set was to maximize selectivity for a given conversion. This also will minimize waste generation in reactors for a given conversion. 

Reactor temperature and pressure. If there is a significant difierence between the effect of temperature or pressure on primary and byproduct reactions, then temperature and pressure should be manipulated to improve selectivity and minimize the waste generated by byproduct formation. d. Catalysts. Catalysts cam have a major influence on selectivity. Changing the catalyst can change the relative influence on the primary and byproduct reactions. 

Feed purification. Impurities that enter with the feed inevitably cause waste. If feed impurities undergo reaction, then this causes waste from the reactor, as already discussed. If the feed impurity does not undergo reaction, then it can be separated out from the process in a number of ways, as discussed in Sec. 4.1. The greatest source of waste occurs when we choose to use a purge. Impurity builds up in the recycle, and we would like it to build up to a high concentration to minimize waste of feed materials and product in the purge. However, two factors limit the extent to which the feed impurity can be allowed to build up ... 

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). 

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