Transpiration reactor

Here in Chapter 1 we make the additional assumptions that the fluid has constant density, that the cross-sectional area of the tube is constant, and that the walls of the tube are impenetrable (i.e., no transpiration through the walls), but these assumptions are not required in the general definition of piston flow. In the general case, it is possible for u, temperature, and pressure to vary as a function of z. The axis of the tube need not be straight. Helically coiled tubes sometimes approximate piston flow more closely than straight tubes. Reactors with square or triangular cross sections are occasionally used. However, in most of this book, we will assume that PFRs are circular tubes of length L and constant radius R. 

Chapter 2 developed a methodology for treating multiple and complex reactions in batch reactors. The methodology is now applied to piston flow reactors. Chapter 3 also generalizes the design equations for piston flow beyond the simple case of constant density and constant velocity. The key assumption of piston flow remains intact there must be complete mixing in the direction perpendicular to flow and no mixing in the direction of flow. The fluid density and reactor cross section are allowed to vary. The pressure drop in the reactor is calculated. Transpiration is briefly considered. Scaleup and scaledown techniques for tubular reactors are developed in some detail. 

Analytical solutions are possible in special cases. It is apparent that transpiration will lower the conversion of the injected component. It is less apparent, but true, that transpired wall reactors can be made to approach the performance of a CSTR with respect to a transpired component while providing an environment similar to piston flow for components that are present only in the initial feed. 

Membrane reactors, whether batch or continuous, offer the possibility of selective transpiration. They can be operated in the reverse mode so that some... 

Suppose an inert material is transpired into a tubular reactor in an attempt to achieve isothermal operation. Suppose the transpiration rate q is independent of and that qL = Qtrms- Assume all fluid densities to be constant and equal. Find the fraction unreacted for a first-order reaction. Express your final answer as a function of the two dimensionless parameters, QtranslQin and kVIQm where k is the rate constant and... 

Use Scalable Heat Transfer. The feed flow rate scales as S and a cold feed stream removes heat from the reaction in direct proportion to the flow rate. If the energy needed to heat the feed from to Tout can absorb the reaction exotherm, the heat balance for the reactor can be scaled indefinitely. Cooling costs may be an issue, but there are large-volume industrial processes that have Tin —40°C and Tout 200°C. Obviously, cold feed to a PFR will not work since the reaction will not start at low temperatures. Injection of cold reactants at intermediate points along the reactor is a possibility. In the limiting case of many injections, this will degrade reactor performance toward that of a CSTR. See Section 3.3 on transpired-wall reactors. 

Piston Flow in Contact with a CSTR. A liquid-phase reaction in a spray tower is conceptually similar to the transpired-wall reactors in Section 3.3. The liquid drops are in piston flow but absorb components from a well-mixed gas phase. The rate of absorption is a function of as it can be in a transpired-wall reactor. The component balance for the piston flow phase is... 

Schematic diagram of Foster Wheeler transpiring-wall SCWO reactor, 79... 

Figure ES-2 is a block diagram of the Eco Logic technology process. The primary treatment destroys the agent and the energetic materials by hydrolysis with caustic or water. Flowever, the hydrolysis products (hydrolysates) must be further treated prior to final disposal. For this secondary step, Eco Logic proposes to use a transpiring-wall supercritical water oxidation (SCWO) reactor design. The following major operations are included ...

A unique feature of the Foster Wheeler SCWO reactor is its full-length transpiring-wall liner, shown in Figure 4-2. Foster Wheeler claims that this liner design protects the reactor walls from corrosion and salt deposition. The reactor liner is fabricated from multiple layers of Inconel 600 assembled in sheets of what the technology provider refers to as platelets to produce transpiration pores. Deionized water is added to the SCWO reactor through transpiration pores in the liner... 

The purpose of the SCWO reactor tests was to demonstrate that a transpiring-wall SCWO reactor can be operated effectively and reliably under conditions that mimic those planned for the full-scale operation at Blue... 

Area 300 is controlled using a distributed control system (DCS). The DCS monitors and controls all aspects of the SCWO process, including the ignition system, the reactor pressure, the pressure drop across the transpiring wall, the reactor axial temperature profile, the effluent system, and the evaporation/crystallization system. Each of these control functions is accomplished using a network of pressure, flow, temperature, and analytical sensors linked to control valves through DCS control loops. The measurements of reactor pressure and the pressure differential across the reactor liner are especially important since they determine when shutdowns are needed. Reactor pressure and temperature measurements are important because they can indicate unstable operation that causes incomplete reaction. 

Two changes in the SCWO system have had a significant impact on safety. The switch from kerosene to a mixture of kerosene and propylene glycol as a feed additive should reduce operational risks, while the change from air to oxygen will introduce a new hazard. Although the committee knows of no previous accidents that would raise safety questions unique to the transpiring-wall SCWO reactor, it has expressed gen-... 

Foster Wheeler Development Corporation (FWDC) has designed a transportable transpiring wall supercritical water oxidation (SCWO) reactor to treat hazardous wastes. As water is subjected to temperatures and pressures above its critical point (374.2°C, 22.1 MPa), it exhibits properties that differ from both liquid water and steam. At the critical point, the liquid and vapor phases of water have the same density. When the critical point is exceeded, hydrogen bonding between water molecules is essentially stopped. Some organic compounds that are normally insoluble in liquid water become completely soluble (miscible in all proportions) in supercritical water. Some water-soluble inorganic compounds, such as salts, become insoluble in supercritical water. 

Under joint sponsorship by the U. S. Army Research, Development and Engineering Center (ARDEC) and the U. S. Department of Energy (DOE), a bench-scale transpiring wall reactor was developed by Sandia National Laboratories, FWDC, and GenCorp Aerojet. The reactor, which uses SCWO, was designed to treat military and other liquid wastes. A commercial application of the technology is in use to destroy munitions, colored smokes, and dyes. SWCO may also provide a viable alternative to incineration for the destruction of chemical weapons. 

The transpiring-waU reactor has the potential to minimize many of the corrosion and deposition problems that have plagued previous SCWO studies. SRCE is developing a proprietary closed-cycle process that recirculates water for SCWO process at full system pressures. The design of the system was developed from previous work with gas turbine and rocket engines. 

Transpired wall reactors Nonideal tubular reactors may have concentrations that vary in the r and 0 directions... 

---