Waste process

The two inner layers of the onion diagram in Fig. 1.6 (the reaction and separation and recycle systems) produce process waste. The process waste is waste byproducts, purges, etc. 

Process operations. The third source of process waste we can classify under the general category of process operations. Operations such as start-up and shutdown of continuous processes, product changeover, equipment cleaning for maintenance, tank filling, etc. all produce waste. 

Sometimes waste streams can be recycled directly, but between different processes. Waste streams from one process can become the feedstock for another. The scope for such waste exchanges is often not fully realized, since it often means waste being transferred between different companies. 

The third source of process waste after the reactor and separation and recycle systems is process operations. 

In continuous processes, all those sources of process waste associated with start-up and shutdown also apply to product changeover in multiproduct plants. 

Process waste minimization in general terms is a question of... 

The major products of combustion are CO2, water, SO, and NO. The products of combustion are clearly beshminimized by making the process efficient in its use of energy through improved heat recovery and avoiding unnecessary incineration through minimization of process waste. 

In Chap. 10, modification of the process for reducing process waste was considered in detail. It also was concluded that to minimize utility waste, the single most effective measure would be improved heat recovery. The energy-targeting methods presented in Chaps. 6 and 7 maximize heat recovery for a given set of process conditions. However, the process conditions can be changed to improve the heat recovery further. 

The purpose of chemical processes is not to make chemicals The purpose is to make money. However, the profit must he made as part of a sustainable industrial activity which retains the capacity of ecosystems to support industrial activity and life. This means that process waste must be taken to its practical and economic minimum. Relying on methods of waste treatment is usually not adequate, since waste treatment processes tend not so much to solve the waste problem but simply to move it from one place to another. Sustainable industrial activity also means that energy consumption must be taken to its practical and economic minimum. Chemical processes also must not present significant short-term or long-term hazards, either to the operating personnel or to the community. 

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). 

In a rotary kiln, the burner can produce both thermal and fuel NO, if the fuel contains nitrogen. Many soHd waste streams also contain nitrogen, typically as much as 20 wt %, which contributes to the fuel NO pathway. Key sources of soHd waste fuel nitrogen include plastics, nylons, dyes, and other process wastes. Nylon, for example, is 33 wt % nitrogen. 

The processing wastes come from the hides and processing chemicals. The hide wastes are the largest problem. For each metric ton of hides received at the tannery the following wastes are generated ... 

Bulk sohds do not always discharge rehably. Unrehable flow, which can occur with some frequency, can be expensive in terms of inefficient processes, wasted product, and operational comphcations. Predictable flow is often impeded by the formation of an arch or rathole, or fine powders may flood uncontroUably. 

A significant use of dkect-process waste is realized by C H -Si bond formation via silylative decarbonylation (Fig. 2) (49,50). A novel route to CgHg—Si bond formation has also been described (eq. 2) (51). 

High density tungsten alloy machine chips are recovered by oxidation at about 850°C, foUowed by reduction in hydrogen at 700—900°C. Typically, the resultant powders are about 3-p.m grain size and resinter readily. There can be some pickup of refractory materials used in furnace constmction, which must be controUed. This process is important commercially. Eor materials that may be contaminated with other metals or impurities, the preferred recovery process is the wet chemical conversion process used for recovery of tungsten from ores and process wastes. Materials can always be considered for use as additions in alloy steel melting. 

The manufacture of vanillin shows the progress made in the chemistry and chemical engineering of the substance. Most commercial vanillin is synthesized from guaiacol the remainder is obtained by processing waste sulfite Hquors. Preparation by oxidation of isoeugenol is of historical interest only. 

List as required) Include in each as required suhstructure, superstructures, Process-waste sewers... 

In addition to many varied apphcations in the chemical industiy, the reactotherm is widelv used to process waste sludges which must be dried in order to lanc fill the sohd components. In many of these cases, the solvents are valuable components of the waste stream and can be recovered and recycled. 

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