Bypass reactor

Failure of a temporary pipe installed two months before as a reactor bypass. 28 Fatalities, 180,000,000 loss... 

As can be seen from Figure 3b and 3d continuous flow systems bypass wastewater and recycle sludge to develop flexibility. Recycling is directed mostly to the first reactor. Bypass flow typically goes to anoxic or anaerobic tanks to supply electron donors for the removal of phosphorus and/or for denitrification. The equivalent action in an SBR is the application of aeration and mixing during react (except after static fill). 

The absorber pump constantly recycled the fluid through the oxygen absorber so that the fluid was always essentially saturated with oxygen. A small side stream was removed from the gas absorber recycle by the reactor pump. The side stream could either flow through the reactor or bypass the reactor. The reactor bypass was used when it was desired to study the decomposition in solution of the humic acids. Down stream from the reactor was a filter to remove any coal fines produced, a sight glass to observe the fluid, a flow colorimeter to measure the rate of production of humic acids, and a flow rate indicator. 

The intensity function curves clearly show the suspected plant reactor bypassing some stagnancy is also indicated. The slight stagnancy of alternative A and the uniform behavior of alternative B are also shown. If ideal stirred tank behavior were superimposed on the plot it would be a horizontal line (this limiting behavior is discussed in the second case of intensity function utility presented later in this paper). 

The primary water specifications for a PWR are given in Table 1 (4). Rigid controls are appHed to the primary water makeup to minimise contaminant ingress into the system. In addition, a bypass stream of reactor coolant is processed continuously through a purification system to maintain primary coolant chemistry specifications. This system provides for removal of impurities plus fission and activated products from the primary coolant by a combination of filtration (qv) and ion exchange (qv). The bypass stream also is used both to reduce the primary coolant boron as fuel consumption progresses, and to control the Li concentrations. 

Process development on fluidized-bed pyrolysis was also carried out by the ConsoHdation Coal Co., culminating in operation of a 32 t/d pilot plant (35). The CONSOL pyrolysis process incorporated a novel stirred carbonizer as the pyrolysis reactor, which made operation of the system feasible even using strongly agglomerating eastern U.S. biturninous coals. This allowed the process to bypass the normal pre-oxidation step that is often used with caking coals, and resulted in a nearly 50% increase in tar yield. Use of a sweep gas to rapidly remove volatiles from the pyrolysis reactor gave overall tar yields of nearly 25% for a coal that had Eischer assay tar yields of only 15%. 

Often, complete mixing cannot be approached for economic reasons. Inactive or dead zones, bypassing, and limitations of energy input are common causes. Packed beds are usually predominantly used in plug flow reactors, but they may also have small mixing zones... 

A stirred tank sometimes can be modeled as having a fraction Ot in bypass and a fraction of the reactor volume stagnant. The material balance then is made up of... 

At high pressure experiments the reactor should be installed in a pressure cell. All check valves before it, and the filter with the flow controller after it, can be kept in the vented operating room. As a minimum, the bypass valve and the flow controller must be accessible to the operator. This can be done by extended valve stems that reach through the protecting wall. Both the operating room and the pressure cell should be well ventilated and equipped by CO alarm instruments. 

The unit was built in a loop because the needed 85 standard m /hour gas exceeded the laboratory capabilities. In addition, by controlling the recycle loop-to-makeup ratio, various quantities of product could be fed for the experiments. The adiabatic reactor was a 1.8 m long, 7.5 cm diameter stainless steel pipe (3 sch. 40 pipe) with thermocouples at every 5 centimeter distance. After a SS was reached at the desired condition, the bypass valve around the preheater was suddenly closed, forcing all the gas through the preheater. This generated a step change increase in the feed temperature that started the runaway. The 20 thermocouples were displayed on an oscilloscope to see the transient changes. This was also recorded on a videotape to play back later for detailed observation. 

The bypass valves control the differential pressure between the reactor and regenerator by varying the flowrate in the expander bypass. 

Using a cooled bypass around the compressor, or by any means possible, try to establish spread between the points. It is amazing how data points can look different and still come back to the same point on the curve when the calculations are complete. If the compressor is tied to a reactor, the points may have to be taken over quite a period of time which can be done if the instruments are maintained. Be careful of fouling when using this method. 

The differential reactor is simple to construct and inexpensive. However, during operation, care must be taken to ensure that the reactant gas or liquid does not bypass or channel through the packed catalyst, but instead flows uniformly across the catalyst. This reactor is a poor choice if the catalyst decays rapidly, since the rate of reaction parameters at the start of a run will be different from those at the end of the run. 

On June 1, 1974, a cyclohexane vapor cloud was released after the rupture of a pipe bypassing a reactor. In total, approximately 30,000 kg of cyclohexane was released. The cyclohexane formed a cloud which ignited after a period of approximately 30 to 90 seconds. As a result, a very strong explosion occurred which caused the death of 28 people and injured 36 people. The plant was totally destroyed and 1821 houses and 167 stores and factories in the vicinity of the plant were damaged. 

In the Flixborough disaster, one of six reactors in series, through which hot cyclohexane was passed, was removed from service (see Figure 2.1). Each reactor was connected by a short pipe with a bellows at each end to allow for expansion. The fifth reactor was replaced by a temporary bypass pipe with two bends in it to allow for differences in height between reactors 4 and 6. Because the bypass was not properly supported and had a bellows at either end, it moved when there were pressure variations. This movement eventually caused the bellows to fail, releasing 50 tons of cyclohexane which exploded, killing 28 men. 

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