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10 Questions You Should to Know about Industrial Reactor

Mar. 03, 2025

Industrial Reactors - Elements of Chemical Reaction Engineering

Liquid Phase Reactions

Semibatch reactors and CSTRs are used primarily for liquid-phase reactions.

A semibatch reactor (Figure 1-1) has essentially the same disadvantages as the batch reactor. However, it has the advantages of temperature control by regulation of the feed rate and the capability of minimizing unwanted side reactions through the maintenance of a low concentration of one of the reactants. The semibatch reactor is also used for two-phase reactions in which a gas usually is bubbled continuously through the liquid.

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A CSTR is used when intense agitation is required. Table 1-1 gives the typical sizes (along with that of the comparable size of a familiar object) and costs for batch and CSTR reactors. All reactors are glass lined and the prices include heating/cooling jacket, motor, mixer, and baffles. The reactors can be operated at temperatures between 20 and 450°F and at pressures up to 100 psi.

The CSTR can either be used by itself or, in the manner shown in Figure 1-2, as part of a series or battery of CSTRs. It is relatively easy to maintain good temperature control with a CSTR because it is well mixed. There is, however, the disadvantage that the conversion of reactant per volume of reactor is the smallest of the flow reactors. Consequently, very large reactors are necessary to obtain high conversions. An industrial flow sheet for the manufacture of nitrobenzene from benzene using a cascade of CSTRs is shown and described in the Professional Reference Shelf for Chapter 1 on the DVD.

If you are not able to afford to purchase a new reactor, it may be possible to find a used reactor that may fit your needs. Previously owned reactors are much less expensive and can be purchased from equipment clearinghouses such as Aaron Equipment Company ( www.aaronequipment.com ) or Loeb Equipment Supply ( www.loebequipment.com/ ).

Gas Phase Reactions

The tubular reactor (i.e., plug-flow reactor [PFR]) is relatively easy to maintain (no moving parts), and it usually produces the highest conversion per reactor volume of any of the flow reactors. The disadvantage of the tubular reactor is that it is difficult to control temperature within the reactor, and hot spots can occur when the reaction is exothermic. The tubular reactor is commonly found either in the form of one long tube or as one of a number of shorter reactors arranged in a tube bank. Most homogeneous liquid-phase flow reactors are CSTRs, whereas most homogeneous gas-phase flow reactors are tubular.

The costs of PFRs and PBRs (without catalyst) are similar to the costs of heat exchangers and can be found in Plant Design and Economics for Chemical Engineers , 5th ed., by M. S. Peters and K. D. Timmerhaus (New York: McGraw-Hill, ). From Figure 15-12 of the Peters and Timmerhaus book, one can get an estimate of the purchase cost per foot of $1 for a 1-in. pipe and $2 per foot for a 2-in. pipe for single tubes and approximately $20 to $50 per square foot of surface area for fixed-tube sheet exchangers.

A packed-bed (also called a fixed-bed) reactor is essentially a tubular reactor that is packed with solid catalyst particles. This heterogeneous reaction system is most often used to catalyze gas reactions. This reactor has the same difficulties with temperature control as other tubular reactors; in addition, the catalyst is usually troublesome to replace. On occasion, channeling of the gas flow occurs, resulting in ineffective use of parts of the reactor bed. The advantage of the packed-bed reactor is that for most reactions it gives the highest conversion per weight of catalyst of any catalytic reactor.

Another type of catalytic reactor in common use is the fluidized-bed reactor, which is analogous to the CSTR in that its contents, though heterogeneous, are well mixed, resulting in an even temperature distribution throughout the bed. The fluidized-bed reactor can only be approximately modeled as a CSTR; for higher precision it requires a model of its own. The temperature is relatively uniform throughout, thus avoiding hot spots. This type of reactor can handle large amounts of feed and solids and has good temperature control; consequently, it is used in a large number of applications. The advantages of the ease of catalyst replacement or regeneration are sometimes offset by the high cost of the reactor and catalyst regeneration equipment. A thorough discussion of a gas-phase industrial reactor and process can be found on the Professional Reference Shelf of the DVD for Chapter 1. The process is the manufacture of paraffins from synthesis gas (CO and H2) in a straight-through transport reactor.

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Frequently Asked Questions About Charging Solids into a Chemical ...

Adding solids into a reactor is a necessary step for virtually all processes in which these types of vessels are used. Whether it&#;s a DDPS glass-lined reactor or one of a different material of construction, almost all include a manway and multiple nozzles to allow access to the vessel&#;s interior. These access points are used to add solids and liquids to the vessel or serve as installation points for accessories and instrumentation. Since solids come in a variety of shapes and sizes (as well as levels of toxicity, sensitivity, etc.), there are multiple options for introducing solids into a reactor. As a company that has extensive knowledge in both glass-lined reactors and solids transfer, we are often asked about best practices and feasibility when it comes to solids charging, particularly with respect to materials that are difficult to move. Following are some frequently asked questions and points to consider when adding solids into a chemical reactor. While some of these answers are specific to our conveying equipment (our Powder Pump system is designed to be installed on a vessel to safely charge solids into a reactor), a lot of these points are likely applicable to other technologies that are used to mix solids and liquids together.

What if I&#;m handling a corrosive product?

When glass-lined reactors are utilized, it normally means the solvents, solids, and/or their reactive products are extremely corrosive. As such, it is critically important that the Materials of Construction (MOC) of the solids transfer system you employ are compatible with your ingredients and/or product. Some examples of common MOC&#;s that are used either totally or in conjunction with one another include:

316L SS
Hastelloy C
Borosilicate Glass
Conductive PTFE or PFA

What if my reactor is under pressure?

In some cases, the reactor or vessel may be under positive pressure. This can be an issue when trying to charge material into the vessel from a container at lower pressure. To help ensure no issues occur during material charging, it is important to use a conveying system that can discharge the material into the reactor at a minimum of 5-10 psig over the vessel&#;s operating pressure. This will help to ensure smooth discharge from a higher pressure zone (solids conveyor) into a lower pressure zone (vessel).

What if I&#;m charging into flammable solvents?

Explosion or deflagration prevention is the key design intent for many conveying technologies and should be a top priority for yours if you are working with volatile chemicals. For a flame to be created, three things are required: fuel, oxygen, and an ignition source. At DDPS, we focus on two of these components &#; oxygen and ignition sources. As it relates to our Powder Pump system:

First, prior to any solid being discharged into the reactor/vessel, oxygen entrained within it is dramatically reduced via the vacuum source. Then, the Powder Pump chamber is backfilled with an inert gas, often nitrogen, to ensure the solids have been safely inerted. After that, the material can safely be discharged into the vessel. Watch a video demonstration of the Powder Pump in action to get a visual understanding of its working principles.
Second, to prevent an ignition source (usually in the form of a static electrical discharge), it&#;s essential that the system is grounded. This is typically the customer&#;s responsibility to ensure a proper connection is made between the conveying system and a local ground. Some systems, like our Powder Pump, can be designed with anti-static and static dissipating components to help minimize the risk of static electrical build-up and discharge.

What if solvent vapors are condensing in the solids addition nozzle and product build up is occurring?

This is a phenomenon that can potentially cause complications in the process. Hare are a couple of ways we at DDPS have addressed this in the past:

Heat tracing around the nozzle - This can help keep the nozzle area above condensation temperatures of the solvents being used. This helps prevent premature exposure of the solids to liquid solvent droplets during discharge through the nozzle.
Secondary isolation valve with purged spool piece - The secondary valve only opens and closes at the beginning and end of solids charging operations. While it is open, a constant supply of inert gas is supplied to the pipe spool between the isolation valve and the Powder Pump system. This flow of low pressure gas helps keep solvent vapors away from the charge nozzle. This solution is specific to our Powder Pump unit and might not apply to other manufacturers&#; solutions. For more details, please feel free to contact us directly.

Is there a way to disperse the material when charging versus dropping in large slugs of material?

Sometimes, discharging relatively large amounts of solids into the reactor one time can make it more difficult to homogenize the mixture before adding the next charge, or possibly overtax the agitator and mechanical seal assembly. To help address this, DDPS provides what we call a &#;dispersion cone&#;. It&#;s an insert that slides into the reactor through the inlet nozzle. When the slug of powder collides with the cone, it helps to better disperse the product in the liquid, making the mixing a bit easier.

What about solids or dust accumulating in my vent line?

Dust accumulation can potentially occur in some smaller diameter vent lines or when handling low bulk density products that don&#;t settle quickly into the liquid. We can provide a vent filter, which is designed to keep these dusts or solids from getting into your vent line.

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