Reactor size reduction

Stankiewicz (40) gives a spectacular example of reactor size reduction by a factor of ca. 100, as a result of replacement of the conventional system with a monolithic reactor operated horizontally in a pipeline. 

Tubular reactors often offer the greatest potential for inventory reduction. They are usually simple, have no moving parts, and a minimum number of joints and connections that can leak. Mass transfer is often the rate-limiting step in gas-liquid reactions. Novel reactor designs that increase mass transfer can reduce reactor size and may also improve process yields. 

Before MPW is fed into the process, a basic separation of the non-plastic fraction and size reduction is needed. This prepared feedstock is then introduced in the heated fluidised bed reactor which forms the core of the process. The reactor operates at approximately 500 °C in the absence of air. At this temperature, thermal cracking of the plastics occurs. The resulting hydrocarbons vapourise and leave the bed with the fluidising gas. Solid particles, mainly impurities formed from, e.g., stabilisers in plastics, as well as some coke formed in the process mainly accumulate in the bed. Another fraction is blown out with the hot gas and captured in a cyclone. 

Calculations predict that improved heat transfer for reacting systems in micro-channel heat-exchanger reactors could lead to considerable size reduction of the equipment, by enhancing the degree of product formation per micro channel (see Figrue 1.24) [140, 141]. This was exemplarily shown for a fast, high-temperature... 

While operating 7000 hr one will be able to process 7000/0.72, or 9722 batches/year. Each batch will then contain 2 x 106/0.97(9722), or 212 lb. The necessary reactor volume will then be 28 gal. Under these circumstances the times necessary to perform the nonreactive operations would undoubtedly be somewhat reduced. One should recognize that these steps will be the bottlenecks in this operation. The required reactor size is definitely on the small side, and it would be preferable to operate in a larger reactor and process a smaller number of batches per year with attendant reductions in labor requirements. 

Intensification Sometimes it is possible to achieve significant reductions in reactor size (and inventory) with improved mixing technology. Another example of intensification is changing from a batch operation to a smaller scale continuous operation. 

Economic and safety considerations have led to reductions in stockpiles of chemicals and decreasing transportation of hazardous substances. Industrially, reactor size is now... 

Tonkovich et al. [123] claimed a 90% size reduction due to the introduction of micro channel systems into their device, which made use of the hydrogen off-gas of the fuel cell anode burnt in monoliths at palladium catalyst to deliver the energy for the fuel evaporation. A metallic nickel foam 0.63 cm high was etched and impregnated with palladium to act as a reactor for the anode effluent It was attached to a micro structured device consisting of liquid feed supply channels and outlet channels for the vapor, the latter flowing counter-flow to the anode effluent... 

Note that we have said nothing about the size of the reactor vessel. If the reactor operates isothermally, the composition profiles shown in Figures 4.18 and 4.19 are independent of reactor size. Of course, attaining a constant-temperature trajectory becomes more difficult as the vessel size increases because of the reduction in area-to-volume ratio. 

The reaction rate, as measured by the current density, is also an important parameter as it determines the reactor size and thus capital cost of the process. To date, researchers have reported moderate to high current densities (200-600 mA-cm 2) using gas diffusion electrodes (GDEs) similar to those used in fuel cells. Further work is thus needed to significantly improve the energetic efficiency and current densities for CO2 reduction. 

We believe the next phase of development of the LP methanol process will relate to reduction in capital costs. This will become particularly significant as plant sizes increase. ICI is dedicated to continued further development of its catalyst to improve activity and life. This will lead to a reduction in the reactor size and catalyst volume and, consequently, to a reduction in capital cost. 

Some preparation of the waste plastics feed is required before pyrolysis, including size reduction and removal of most nonplastics. This feed is charged into the heated fluidized bed reactor, operating at 500°C, in the absence of air. The plastics thermally crack to hydrocarbons, which leave the bed together with the fluidizing gas. Solid impurities and some coke either accumulate in the bed or are carried out as fine particles and captured by cyclones. 

Combined with the use of precious metal catalyzed washcoats deposited on the walls, microchannel reactors can realize nearly 10 times reduction in reactor size compared with that of a process that utilizes catalyst particles. The washcoat thickness is usually less than lOOjit and provides greater structural stability. This stability arises from smaller thermal expansion ratios and lower temperature gradients. 

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