Stripping steam venting

Usually, only a small amount of the heating steam—specifically, stripping steam—is vented through the restriction orifice, out the atmospheric vent. It is this small stripping steam flow that drives the air out of the soft water. 

The vapor stream from the meal and oil distillation systems consists of solvent vapor, water vapor (from the stripping steam) and air that has entered the system entrained in the voids of the press cake. Some additional air unavoidably gains entry into the vacuum systems. The vapor stream from the final condenser consists of air saturated with solvent and water vapors. The solvent vapors are selectively scrubbed in a packed tower by a counterflow of special mineral oil. The mineral oil is recycled after being heated, stripped of solvent, and cooled. The hexane vapor remaining in the vent stream should be below the lower explosive limit (1.3% by volume). Nevertheless, overall rapeseed plant losses per tonne flow through the extractor are typically much higher than they are for soybeans. This problem should be researched and, if possible, overcome. 

This carbon dioxide-free solution is usually treated in an external, weU-agitated liming tank called a "prelimer." Then the ammonium chloride reacts with milk of lime and the resultant ammonia gas is vented back to the distiller. Hot calcium chloride solution, containing residual ammonia in the form of ammonium hydroxide, flows back to a lower section of the distiller. Low pressure steam sweeps practically all of the ammonia out of the limed solution. The final solution, known as "distiller waste," contains calcium chloride, unreacted sodium chloride, and excess lime. It is diluted by the condensed steam and the water in which the lime was conveyed to the reaction. Distiller waste also contains inert soHds brought in with the lime. In some plants, calcium chloride [10045-52-4], CaCl, is recovered from part of this solution. Close control of the distillation process is requited in order to thoroughly strip carbon dioxide, avoid waste of lime, and achieve nearly complete ammonia recovery. The hot (56°C) mixture of wet ammonia and carbon dioxide leaving the top of the distiller is cooled to remove water vapor before being sent back to the ammonia absorber. 

This reaction can also be mn in a continuous fashion. In the initial reactor, agitation is needed until the carbon disulfide Hquid phase reacts fully. The solution can then be vented to a tower where ammonia and hydrogen sulfide are stripped countercurrendy by a flow of steam from boiling ammonium thiocyanate solution. Ammonium sulfide solution is made as a by-product. The stripped ammonium thiocyanate solution is normally boiled to a strength of 55—60 wt %, and much of it is sold at this concentration. The balance is concentrated and cooled to produce crystals, which are removed by centrifiigation. 

Air emissions from a petroleum distillation unit include emissions from the combustion of fuels in process heaters and boilers, fugitive emissions of volatile constituents in the crude oil and fractions, and emissions from process vents. The primary source of emissions is combustion of fuels in the crude preheat furnace and in boilers that produce steam for process heat and stripping. When operating in an optimum condition and burning cleaner fuels (e.g., natural gas, refinery gas), these heating units create relatively low emissions of sulfur oxides, (SO c), nitrogen oxides (NO c), carbon monoxide (CO), hydrogen sulfide (H2S), particulate... 

Air emissions may arise from fugitive propane emissions and process vents. These include heater stack gas (carbon monoxide, sulfur oxides, nitrogen oxides, and particulate matter) as well as hydrocarbon emission, such as fugitive propane and fugitive solvents. Steam stripping wastewater (oil and solvents) and solvent recovery wastewater (oil and propane) are also produced. 

A small amount of steam is vented from the top of the stripping tower to the atmosphere. Using a gate valve, with a hole drilled through the gate, is a simple way to control the venting rate. The dissolved air in the cold BFW is vented with this steam. 

Devolatilization. Following polymerization of many polymers, removal of residual monomer or solvents is necessary. Ultimately this removal becomes controlled by diffusion from the polymer no matter what type of process is employed (27). Many processes use a steam-stripping operation for this purpose, and others employ devolatilization in a vented extruder. Removal of residual vinyl chloride monomer from poly(vinyl chloride) was an issue of much concern following the discovery that this monomer is a carcinogen. 

The first stage consists of five parallel groups of two series-connected towers, of which one group, lA and IB, are shown in Fig. 13.3. Feed for each lA tower consists of condensate from the reboiler of the associated IB tower. Feed is introduced at the top of the lA tower. Stripped vapor from the top plate is condensed in a barometric condenser, vented to a steam qector that maintains a pressure of from SO to 90 Torr at the top of the tower. 

The process is much the same as that described in Section 9.1.9.1 but is on a much larger scale. After absorption of 99.8% of the chlorine, the remaining gas, boosted by an ejector if necessary, is scrubbed with caustic before venting. The chlorine is recovered from the solvent by steam stripping and condensation against cooling water. The stripped solvent, after cooling, returns to the absorber. The process also requires some means to prevent the loss of solvent and keep it out of the product chlorine. 

The recovery of solvent from both the miscella and the leached seeds or beans is an essential part of the vegetable-oil leaching process. In a typical arrangement, the filtered miscella is passed to an evaporator for removal of solvent, sometimes followed by final stripping in a tray column, to produce the solvent-free oil. The wet seeds are steamed to remove residual solvent and air-cooled. Vented gas from condensers may be sent to an absorber to be scrubbed with petroleum white oil, and the resulting solvent-white-oil solution stripped to recover any solvent. 

The steam and cold deaerator makeup water mix in the small stripping section shown in Fig. 22.6. Most of the steam condenses (typically 90 percent) to heat the cold water (120°F) to its boiling point temperature (250°F) at the deaearator operating pressure of 15 psig. The rest is vented to the atmosphere. This vented steam is being used to strip out the residual in the cold-water feed. 

As I ve described in my book. Troubleshooting Process Plant Control, any time the steam inlet control valve becomes fully open, the deaerator temperature, pressure, and water level will become unstable and the deaerator stripping section will flood. Flood in the sense that boiling water may erupt from the atmospheric vent. 

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