Processing heat exchange

Following the pinch rules, there should be no heat transfer across either the process pinch or the utility pinch by process-to-process heat exchange. Also, there must be no use of inappropriate utilities. This means that above the utility pinch in Fig. 16.17a, high-pressure steam should be used and no low-pressure steam or cooling water. Between the utility pinch and the process pinch, low-pressure steam should be used and no high-pressure steam or cooling water. Below the process pinch in Fig. 16.17, only cooling water should be used. The appropriate utility streams have been included with the process streams in Fig. 16.17a. 

Cooling loads can be transferred from process heat exchangers to a wastewater-evaporation system, thus reducing cooling-water requirements and total wastewater volume. 

The design of a process heat exchanger usually proceeds through the following steps ... 

Fluid-Elastic Coupling Fluid flowing over tubes causes them to vibrate with a whirling motion. The mechanism of fluid-elastic coupling occurs when a critical velocity is exceeded and the vibration then becomes self-excited and grows in amplitude. This mechanism frequently occurs in process heat exchangers which suffer vibration damage. 

Where cooled or warmed liquids leave a process, heat exchangers can provide the means of pre-cooling or pre-warming fresh liquids entering. One of the main instances of this is the warm waste water from showers in changing rooms. 

Oxygen and ammonia together create a serious problem. Copper and brasses used in surface condensers, LP FW heaters, fan-coil space heating units, and process heat-exchangers are particularly vulnerable, as... 

Fins are used to increase the effective surface area of heat-exchanger tubing. Many different types of fin have been developed, but the plain transverse fin shown in Figure 12.66 is the most commonly used type for process heat exchangers. Typical fin dimensions are pitch 2.0 to 4.0 mm, height 12 to 16 mm ratio of fin area to bare tube area 15 1 to 20 1. 

Kern and Kraus (1972) give full details of the use of finned tubes in process heat exchangers design and design methods. 

Hot oil is heated in a furnace in three parallel passes. The oil is used as a heat source in four parallel process heat exchangers. Draw a control concept diagram that achieves the following objectives ... 

A valve position controller is used to reset the setpoint of the furnace exit temperature controller such that the control valve that is the most open of the four control valves on the hot oil streams flowing through the process heat exchangers is 80 percent open. 

Uses. Dielectric in capacitors and transformers investment casting processes heat exchange fluid hydraulic fluid no longer produced in the US... 

V. Cavaseno et al. (Eds.), Process Heat Exchange, McGraw-Hill, New York, 1979. 

In normal operations, continuously recirculating water picks up waste heat from a refrigeration compressor or process heat exchanger, and the hot water is pumped to the top of the tower and dropped over the cooling tower. Evaporative action removes the heat from the water and adds it to the air. The hot, moist air is ejected from the fan stack, and the cooled water returns to the compressor or exchanger to pick up more heat. Figure 1.1 illustrates the cooling tower operation. 

The overhead from the second stage is heated by an exchange with hot solvent. The fired heater further raises the temperature of the solvent/demetallized oil mixture to a point above the critical temperature of the solvent. This causes the demetallized oil to separate. It is then flashed and steam-stripped to remove all traces of solvent. The vapor streams from the demetallized oil and asphalt strippers are condensed, dewatered, and pumped up to process pressure for recycle. The bulk of the solvent goes overhead in the supercritical separator. This hot solvent stream is then effectively used for process heat exchange. The subcritical solvent recovery techniques, including multiple effect systems, allow much less heat recovery. Most of the low grade heat in the solvent vapors from the subcritical flash vaporization must be released to the atmosphere requiring additional heat input to the process. 

Figure 3 A process heat exchanger assembled from ion beam mixed plates...

Kim, Y-W., et al. (2008), Development of a Coupling Process Heat Exchanger Between a VHTR and a Sulphur-iodine Hydrogen Production System , Proc. of HTR2008, Washington, DC, USA, 28 September-1 October. 

In the CEA process, heat exchange with the sulphur section takes place between 900 and ca. 600°C, whereas heat exchange with the iodine section takes place between around 600 and 400°C. In the GA process, no nuclear heat exchange with the iodine section exists, allowing thus a higher return temperature (590°C instead of 400°C). Figure 5 depicts Q.-T curves for the GA Section II. 

Process heat exchanger failure Damage of SSC Fuel and primary system corrosion... 

JAEA conducted an improvement of the RELAP5 MOD3 code (US NRC, 1995), the system analysis code originally developed for LWR systems, to extend its applicability to VHTR systems (Takamatsu, 2004). Also, a chemistry model for the IS process was incorporated into the code to evaluate the dynamic characteristics of process heat exchangers in the IS process (Sato, 2007). The code covers reactor power behaviour, thermal-hydraulics of helium gases, thermal-hydraulics of the two-phase steam-water mixture, chemical reactions in the process heat exchangers and control system characteristics. Field equations consist of mass continuity, momentum conservation and energy conservation with a two-fluid model and reactor power is calculated by point reactor kinetics equations. The code was validated by the experimental data obtained by the HTTR operations and mock-up test facility (Takamatsu, 2004 Ohashi, 2006). 

Sato, H., et al. (2007), Conceptual Design of the HTTR-IS Hydrogen Production System - Dynamic Simulation Code Development for the Advanced Process Heat Exchangers in the HTTR-IS system , Proc. of International Conference on Advanced Fuel Cycles and Systems (GLOBAL2007), Boise, ID, USA, pp. 812-819. 

FIGURE 1 Typical temperature profiles for several process heat exchanger applications (a) product cooler (b) feed heater with condensing stream (c) multicomponent feed heater with vaporization and superheating (d) pure-component product condenser (e) multicomponent product condenser (f) typical feed-effluent heat exchanger. 

---