Control Valve Sourcebook — Chemical Process Overview Reactor

Control Valve Sourcebook — Chemical Process Overview

Reactor

Topic Page I How it Operates 2 II Where Reactors Are Used 3 III Reactor Application Review 4 Reactor

Plug Flow Reactor (PFR) Reactor This reactor is primarily used for gas-phase reactions. It is modeled and designed after a “plug flow profile.” The I. How It Operates conversion of chemicals is also reliant of the reactor volume. This reactor has tubes that the feed (gases and/or liquids) A chemical reactor is a vessel designed to contain reactions travel through at high velocity. This helps with mixing and in order to produce a desired product. Listed below are the causing the feed to take a long path through the reactor. most common types of reactors and methods of operation. Hence, more time for the feed to be converted into desired Types of reactors: products. Refer to Figure 2 for a representation of PFR. Continuous stirred tank Plug flow reactor Packaged bed reactor (fixed or fluidized) Methods of operations: Batch Continuous Semi-continuous Types of Reactors

Continuous Stirred Tank (CSTR) The CSTR reactor is primarily used for liquid-phase reactions. As the name suggests, it is stirring to attempt perfect mixing. The conversion of the chemical is dependent on the E1706 volume of the reactor. Figure 1 shows a representation of a CSTR. Figure 2. Representation of a PFR Each reactor will have a fixed volume which also means it will have a fixed residence time. Knowing these two values feed rate can be controlled accurately. Packed Bed Reactor (PBR)

REACTANT 1 A PBR can be either fluidized or fixed bed and is primarily REACTANT 2 used for gas-phase reactions. The conversion in this reactor is dependent on the mass of the catalyst. CONTROL VALVES The fixed bed reactors are packed with solid catalyst and as reactant passes through the catalyst, reaction takes place. TO VENT SYSTEM The fluidized bed reactor consists of plates with catalyst. These catalyst particles behave like fluid as gas flows FLOOR LEVEL through it. Refer to Figure 3 for a representation of fixed bed and a fluidized bed reactor.

COOLANT

STIRRER

PRODUCT E1705 OUTLET

Figure 1. Representation of a CSTR

2 Reactor

GAS II. Where Reactors Are Used PRODUCTS AND UNREACTED MATERIALS Reactors are considered the heart of almost all industrial TO SEPARATE chemical plants. Without these reactors, new products will SOLID not be produced. Figure 4 and 5 display a few examples of industries utilizing batch method and continuous method. CATALYST ON SUPPORT SOLID GAS BUBBLE ADHESIVES SOLID PARTICLE DISTRIBUTOR

SPECIALTY GAS CHEMICAL FINE CHEMICALS PRODUCT FLUID BED DIFFUSER WITH GAS FLOW ACRYLATE MONOMERS

REACTANTS E1707 FOOD BATCH FERMENTATION Figure 3. Fixed bed and fluidized reactor & BEVERAGE Methods of Operations ETHANOL FERMENTATION Batch

Batch process is a closed system typically carried out in WASTE WATER a CSTR. It operates under unsteady state, which means TREATMENT composition changes with time, however, the composition E1708 throughout the reactor is uniform. In a batch process, a Figure 4. Typical chemical industries using the batch method defined quantity of input is fed to the reactor where reaction takes place while the process is controlled under certain CONVERSION OF AROMATIC temperature, pressure, and/or pH. Temperature is typically PARAFFINIC/NAPHTHENIC REFORMING regulated via the heat exchanger. Refer to Figure 6 for a TO AROMATICS layout of a batch process REACTION BETWEEN This reactor method is usually used in small-scale AMMONIA HYDROGEN AND NITROGEN production, and/or new process testing. This reactor could TO FORM AMMONIA also be used when it is difficult to achieve continuous operation conversion. The advantages of this method are OXIDATION OF AMMONIA CONTINUOUS NITRIC ACID high conversion and operation flexibility. TO NITROGEN

Continuous REACTION OF METHANE HyCo AND STEAM TO YIELD Continuous process is typically operated under steady state HYDROGEN condition. In this process, reactants are fed to the reactor at E1709 constant rate and, at the same, rate desired products and byproducts are exiting the reactor. Figure 5. Typical chemical industries using the continuous This reactor method is typically used in large scale method continuous production plants most commonly used in petrochemical, and agrichemical industry. In this method feedstock is constantly moving through a reactor yielding constant flow of product. Similar to the batch reactor controlling pressure, temperature and flow rate will help to optimize the process.

Semi-Continuous The semi-batch reactor is operated with both continuous and batch inputs and outputs. This process is loaded with a batch that produces a product that must be removed continuously. Controlling pressure, temperature, flow rate, and pH will help to optimize the process.

3 Reactor III. Reactor Application Review Typical valve selection: —— Fisher Vee-Ball valve, Baumann 24000 valve, Fisher In this section, a typical setup of a batch process and one GX valve example of a continuous process will be covered. —— Class V shutoff may be utilized to minimize leakage —— Materials of construction: Steam application Batch Process materials or materials compatible with the heating/ cooling medium Figure 6 shows a layout of the reactor set up under a vacuum. Vacuum Control Valves THERMAL OXIDIZERRemoval of certain components during a reaction may be RECOVER / KNOCK OUT DRUM RAW MATERIAL / required. Therefore, batch reactors may be under a vacuum REACTANT ADDITION and maintaining a consistent level of vacuum becomes NITROGEN important. A vacuum control valve can assist to provide a consistent level. If an ejector system is utilized, a load valve STEAM / WATER may also be needed to decrease vacuum levels.

REACTOR JACKET DRAIN Typical valve selection —— Fisher Control-Disk™ valve, Fisher Vee-Ball valve,

E1710 REACTOR DISCHARGE Baumann 24000 valve, Fisher GX valve Figure 6. Set up of Batch Reactor —— Materials of construction are dependent on the process design

Batch reactors demand several objectives in addition to Continuous Process continuous reactors such as: Fast and accurate charging Continuous reactors take several forms, but the common Fast heat-up or cooldown to a new set point without objectives include: oscillation and minimal overshoot —— Holding temperature within a certain margin from the desired set point Stable response to load disturbances —— Minimize operator intervention Since batch reactors are used to create a large variety of —— Minimize consumption of utilities chemical products, control valve selection is dependent upon the fluid being controlled and process control needs. Feed Control Valve Batch Charging Valve Due to the high flow rates common to continuous processes, feed control valve selection is important. These Charging a batch may include the use of a single or multiple valves are responsible for maintaining the right ratio of lines depending upon batch needs. Faster charging can reactants for high yields. Globe valves are commonly utilized reduce batch cycle time, but must be done accurately to due to precise control needs. ensure quality targets are met. Use of a charging valve allows for rate control to ensure accurate batch charging. Temperature Control Valve Typical valve selection: Temperature control valves are another critical control —— Fisher Vee-Ball™ valve, Baumann™ 24000 valve, Fisher valve application in continuous reactions. They must adjust GX valve quickly to process changes with minimal over/under shoot. —— Materials of construction: CF8M or high nickel alloy A more common application is fuel gas control to furnace with corresponding trim (300-series stainless or high burners. Valve selection can depend on burner control nickel alloy) needs, but globe valves are commonly selected for precise control. —— Class V or VI may be required depending on isolation needs For additional information on continuous reaction control valve needs, Reference: Temperature Control Valves Pyrolysis process D352317X012 Batch temperature is a critical control variable that impacts quality, production rates, and operating costs. Control during initial reaction and cooldown typically requires some additional control parameters and can impact valve selection. Response to an exothermic reaction must be stable to maintain setpoint. Split ranging is a common configuration for temperature control utilizing two control valves. Selection of these two valve is important to minimize dead zones in the split range strategy.

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