Process Engineering Equipment Handbook 2009 Part 8 pot

FIG. C-428 Performance and frequency response curves for different I/P converters. (Source: J.M. Voith GmbH.) C-400 FIG. C-429 Performance and frequency response curves for different I/P converters. (Source: J.M. Voith GmbH.) C-401 system. Each mining, power, or paper company has to choose parts for its pipeline that offer the best balance of performance characteristics for its particular load. Knife-gate valves control the flow in many process piping systems. Mining companies use piping systems to transport newly mined minerals, such as gold, ore, and coal, to processing plants. The excavated materials are crushed and suspended in a liquid slurry. An efficient slurry handling system is crucial to timely mineral processing, which is necessary for fast delivery. The slurry flow can be very abrasive and corrosive to the hundreds of valves directing its materials. In mining, newly crushed ore has a sharp surface, can be quite hot, and flows quickly, constantly, and often at high pressure. A slurry valve must be designed for these conditions to reduce maintenance time and replacement costs. (See Fig. C-430.) Power companies, meanwhile, transport different materials, putting their own set of demands on the line’s components. One valve OEM, Clarkson Co., USA, has simulated its valve in action to test how variations in material and design of the product will hold up under different pipeline stresses. This OEM designs and manufactures knife-gate and control valves that can halt and isolate sections of a slurry flow. Efficient control is necessary when the slurry must be delayed, inspected, or redirected. Knife-gate valves are also used in other applications, including industrial scrubber systems, waste-water treatment systems, and industrial process water systems. This OEM’s latest knife-gate designs are referred to as wafer-type valves because they are lighter and thinner than their predecessors, although they can handle higher pressures. The narrower valve fits tighter spaces and gives pipeline designers more flexibility. Wafer-type valve dimensions meet a nationwide standard, providing greater flexibility in choice of supplier because the valves are interchangeable. The knife-gate valve has a blade-like steel gate that lowers into the slurry flow to create a bubble-tight seal. See Fig. C-431. The valve has two matching, smooth elastomer sleeves that seal the blade when the gate is closed and seal each other when the valve is open, so the slurry can flow through unobstructed. The elastomer sleeves are designed to resist abrasion and corrosion and to cover the valve’s metal par´ts to shield them from wear. FIG. C-430 Computer simulation software was used to simulate the valve in action on a computer, reacting to the severe pressure and temperature of the slurry piping system’s flowing materials. (Source: Clarkson Co.) C-402 Controls, Retrofit Controls, Retrofit C-403 The knife-gate valve was a new concept when it was introduced because it replaced conventional metal seats and gate guides with easily replaceable snap-in elastomer sleeves, which are more durable and versatile, and handle higher pressure and temperature. Conventional metal seats and gate guides can fill with hardened slurry and then fail to open or close. Pipeline operators value the elastomer’s long life because each seal costs between $75 and $500 to replace. More important, they lose revenue when they suspend the slurry system for maintenance repairs. This OEM wants to develop a greater variety of elastomer seals for the wafer- type valve to increase its efficiency and reliability in different applications. For example, power companies prefer synthetic types of elastomers like neoprene, butyl or viton, which handle high temperatures and corrosive materials, while mining companies prefer elastomers like natural gum rubber for abrasive slurries. Control, of (Fuel) Manifold Flow* Stepper motor–driven valve In the control of fuel flow to fuel manifolds in a gas turbine, the advent of the stepper motor–driven valve has brought about more accurate control of fuel supply to a gas turbine, with increased safety of operation, simplicity of piping design (see Fig. C- 432), and reduced time between overhauls for the gas turbine. This is by no means the only application for a stepper motor–driven valve, which is popular now in many processes and also in aviation applications. Case study: stepper valve usage. The Petrochemical Corporation of Singapore (PCS) was initially discouraged from producing independent power in excess of its needs. Singapore Power (SP) has preferred to continue to receive the high tariffs paid by its consumers rather than administrate the buyback of small amounts of FIG. C-431 To increase its efficiency in different applications, a greater variety of elastomer seals for the wafer-type knife-gate valve were developed. (Source: Clarkson Co.) * Source: Claire Soares, adapted from 1998 article written on “stepper” valves, PCS, and turbine fuel flexibility for Asian Electricity. power from several small power producers (SPPs). However, now the move toward deregulation is changing that. “Pool rules for small generators,” which covered generators of less than 10 MW and industrial in-house generators (“autogenerators”), were instituted in Singapore as of April 1, 1998. An SPP such as PCS does not have the benefit of steady load, and the quality, type, and heating value of their fuels will vary. This is because they use process gases and fluids for fuel whenever they can, especially if that is the most cost- effective use for a process fluid. Due to the variations in the different characteristics of these fuels, which are in essence different process streams, a very fast response valve is required. Without such a valve, the exhaust gas thermocouples on the gas turbine would note larger swings in turbine exhaust temperature. The key to PCS’s successful use of process fluids—which it didn’t have much other use for—as fuel is valve response time and actuation characteristics. An ideal valve for this type of application is a “stepper” valve or its equivalent. C-404 Controls, Retrofit BEFORE AFTER GAS SUPPLY SHUT OFF VALVE SPEED RATIO VALVE GAS FLOW CONTROL VALVE SRV GCV SOV HYDRAULIC PRESSURE GAS SUPPLY ELECTRIC SHUT OFF VALVE STEPPER GAS FLOW CONTROL VALVE ENGINE MANIFOLD ENGINE MANIFOLD FIG. C-432 “Before” and “after” schematics showing how retrofit of a stepper value can simplify the piping and control system into a gas-turbine engine fuel manifold. (Source: HSDE.) Controls, Retrofit C-405 The stepper valve and functional equivalents. The stepper (short for stepper motor– driven) valve is a fast-response, electrically operated valve that was pioneered by Vosper Thornycroft (HSDE, UK) in the mid-1960s. Now this valve type is made by other well-known manufacturers too, such as Moog, in Germany. The term stepper actually refers to the motor type that drives the valve as opposed to the valve itself. The motor is a stepper motor, as opposed to a torque or AC or DC motor. Its self- integrating function ensures that the valve will proceed to a desired position and then the motor will stop. With other motors, the motor has to continue to run in order to keep the valve in that position—such valves need signals to cue them: run, stop running, then start running again, and so forth. If something were to happen causing the valve to fail, the stepper-type valve position would still lock and the system would continue running. The valve then makes the system fault tolerant, which is critical in applications such as emergency power-supply generators. It also provides the fast response required by aeroderivative and some industrial gas turbines. This is useful for both power generation and mechanical drive service. Before the stepper valve was introduced in the mid-1960s, hydraulic and pneumatic actuation valves were used to provide the required response time. This increased the overall complexity of the fuel system. As always, with instances where system complexity is heightened, system cost increased but mean time between failures (MTBF) and availability decreased. The valve takes up very little space on the installation and service people unused to this new design spend frustrated time looking for the extensive “old” equivalent control system. Development of valves that could compete with HSDE’s original stepper arose from competition with that early design. As a result, there are now many manufacturers who produce functional equivalents on the market for use in gas- turbine fuel systems, high-resolution controls for robots, automatic machining controls, and so forth. In PCS’s application, they use a Moog (German manufacturer) valve that has a DC motor. To get the same “stay in position” feature as a stepper- type valve would have, manufacturers typically use a spring to hold a position. Design aims of fast response valves. The original design aims of the stepper-type valve and its equivalents generally include the following safety considerations: ᭿ A fail-freeze or fail-closed option, depending on whether the operator is a power- generation facility (“freezing” at the last power setting is then required) or a pipeline (in which case turbine shutdown on valve failure is required). ᭿ The liquid fuel version of the valve incorporates a pressure-relief valve protecting the system against overpressure and the fuel pump running on empty or “deadheading,” caused by closure of valves downstream of the fuel valve during system operation. ᭿ High-speed response of less than 60 ms required by aeroderivative gas turbines to prevent overspeed in block off-load conditions. ᭿ Explosion-proof actuation to appropriate specification standards allows operation in hazardous methane service. ᭿ Resistance to fuel contaminants, including tar, shale, water, sand, and so forth. ᭿ Twenty-four volts DC is the maximum drive voltage that ensures personnel safety ᭿ Corrosion resistance in components exposed to wet fuel and to all parts if the service is sour gas. Operational objectives of fast-response valves. Other operational objectives that dictate design features are operator’s requirements for: ᭿ Low mean time to repair (LMTR). The target of 1 h, achieved with modular design, together with the target MTBF provided an availability of 99.998 percent for HSDE’s original stepper. ᭿ Higher MTBF. (In HSDE’s case, an initial development target of 50,000 h was set and achieved.) ᭿ Low maintenance costs, since the modular design can be repaired by an individual with relatively little experience. Service intervals are 12 months. ᭿ Large control ratio that allows control over the ignition to full load as well as full-speed ranges to be possible with one fuel valve. Fuel pressure variation compensation is provided. The additional speed ratio–type control valve found in many other industrial gas fueled installations is not required here. ᭿ Low power consumption since an electric motor of less than 100 W is used. This also eliminates the need for additional hydraulic or pneumatic systems. Also, black starting is more reliable if the fuel system is powered by the same batteries as the controller. A generic stepper valve system can consist of the following items: ᭿ Transformer ᭿ Power supply ᭿ Controller ᭿ A rack ᭿ A DC motor The motor, a brushless servomotor, is generally an electronically commutated three- phase motor with permanent magnet excitation on a low-inertia rotor. The stator’s three-phase windings have thermistor protection. Sinusoidal back electromotor force (emf) provides improved low-speed performance and higher efficiency. The integral brushless resolver provides position feedback so no tachogenerator, mechanical commutator, or electronics within the motor are required. Bearings are preloaded and sealed with high-temperature grease. A static load holding brake is an option. Applications experience. Power production in phase II of the Petroleum Corporation of Singapore was commissioned in June 1997. PCS is part of a massive petrochemical plastics conglomerate in Singapore. Power production was an afterthought, since when they were built, its design did not include provision for becoming an SPP. PCS chose a nominally 25-MW (23 MW in their normal ambient conditions) Alstom GT10, although their power needs are roughly 26 MW. This was because while SP were pleased to sell them their residual requirement, they would not buy any power from SPPs at the time of original power plant design. The turbine is fueled by three different types of fuel, depending on the state of the plant. The British thermal units for each type varies, so again the fast response time for the stepper valve is critical. As PCS operations found, the fast response valve proved as useful as the stepper valve has been for power generation on the North Sea oil and gas platforms. The fast response time of the stepper valve design helps the valve avoid the sudden burst of excess temperatures that accompany higher heating value fuel. (North Sea platform users frequently operate gas, liquid, or gas and liquid fuel mixtures.) Not all gas turbines are tolerant of a wide range of fuel types in a single application. Some of them require a whole different fuel system—nozzles, lines, and C-406 Controls, Retrofit all components—to be able to handle a totally different heating value fuel. In this application in Singapore, the Alstom machine shows no sign of distress, which is interesting since the heating value of the fuel types varies as much as 50 percent. The exact fuel composition data are proprietary to PCS only; however, the GT10 operational data chart, figures, and curves here provide data for typical power output with light oil and natural gas fuel. The rest of the data is typical for the GT10. PCS’s GT10 heat-recovery steam generator (HRSG) provides a reliable source of steam. The plant exports steam to the nearby Seraya Chemicals plant in addition to fulfilling its own needs. The turbine. The relatively low turbine-inlet temperature of the GT10 is one of the keys to being able to use three different fuel streams that exhibit a divergence of 50 percent in terms of heating value, without any noteworthy surges in performance or reductions in hot section component lives. As already described, valve-response speed is another critical feature for ensuring the stability of this application. Emissions and steam supply. The Alstom EV burner—a low NO x burner that can be fitted and retrofitted on the GT10, fuel types permitting—was not fitted in this case. The EV burner will handle clean natural gas and clean diesel fuel. It was not suitable for the high hydrogen content and variations in fuel composition that this application involves. Such fuels need a more forgiving fuel system, as well as water or steam injection to keep the NO x down. The PCS Singapore application uses steam for NO x reduction purposes. The steam is piped in through nozzles that are adjacent to the fuel nozzles on the fuel manifold of the GT10’s annular combustor. The source of the steam is the HRSG that is packaged as part of the GT-10 system. If and when required, the plant also can draw high-pressure steam from its process cracker. In PCS’s case, one boiler has been found to suffice. This is noteworthy as in applications such as this, a redundant “packaged boiler” (running hot and on minimum load) is often found essential. This is so that it is possible to pick up the steam load should the turbine trip or be unavailable due to maintenance. A common subject for debate is whether uninterrupted steam supply during the switch from HRSG mode to fresh-air firing is possible without flameout on the boiler supplementary burners. The PCS plant is part Japanese owned, so the specifications the installation had to meet matched those of environmentally particular Singapore, as well as the Japanese, who are the most environmentally strict practitioners in Asia. Steam injection reduces NO x levels from 300 to 400 mg/MJ fuel to just below 100 mg/MJ fuel. (Note: As the upstream company PCS’s main role is to supply high-quality ethylene, propylene, acetylene, and butadiene, as well as utility services such as water, steam, and compressed air, to downstream companies, PCS directly produces and exports benzene, toluene, and xylene for global markets.) Future potential for power generation in Singapore. The pressure for accelerated deregulation is increasing in Singapore as well, if not as fast as in the rest of southeast Asia. Singapore Power is gradually seeing more IPP contracts let in the country. SPC’s experience with the GT10 they operate has been positive in terms of availability and maintainability. Just as important is this gas turbine’s ability to use three different “waste” petrochemical fluids as fuel, despite the 50 Controls, Retrofit C-407 percent difference of these three fluids in terms of heating value. That it can do this while maintaining NO x emissions below legislated limits for countries as environmentally strict as Singapore, speaks well for its continued use in similar applications. Conversion Tables (see Some Commonly Used Specifications, Codes, Standards, and Texts) Conveyors* (see also Drives; Power Transmission) With numerous process plants employing conveyors of one type or another, it was felt that this text should give at least an introduction to this type of machinery by focusing on one of the more sophisticated executions: steel-belt conveyors. The use of steel-belt conveyors has spread throughout the processing industries. Applications of steel-belt conveyors include cooling/solidification, drying, pressing, freezing, baking, and materials conveying. The steel belt is made from flat strip steel from a rolling mill, prepared through special techniques that straighten, flatten, and make the ordinary strip suitable for welding into endless bands continuously running around two terminals. The conveyors based on this specialized technology are designed for the processing industries according to the needs of the product and the special needs of the steel belt. Table C-34 summarizes a wide variety of steel-belt applications and the important steel-belt properties that make the applications successful. The general categories that are shown in Table C-34 are material handling, food processing, industrial processing, and presses for particle boards, plastics, and rubber. Table C-34 also indicates the four major steel-belt grades that are in common use. The following discussions describe the applications and processes for which steel- belt conveyors have been selected as the best of competing alternatives, including the types of materials used for conveyor belts. Reference and Additional Reading 1. Bloch, H., and Soares, C. M., Process Plant Machinery, 2d ed., Butterworth-Heinemann, 1998. Coolant; Engine Coolant The number of coolants available on the market is large. For illustrative purposes, the common one chosen here is propylene glycol. The discussion that follows † indicates the characteristics sought in most coolants. Circulation of Coolant through a Typical Engine Coolant circulates through passages in the engine block surrounding the cylinders. Coolant also flows through the cylinder head to cool the valves and combustion chamber area. The heated coolant then flows through a thermostat to either the radiator to be cooled or to the coolant pump for circulation back to the engine. (See Fig. C-433.) C-408 Conversion Tables * Source: Sandvik Process System, Inc., USA. † Source: ARCO Chemical, USA. [...]... Testing Laboratories, Report # 532015 Applies to models AHP- (1,200XP, 1,200XPHC, 1 ,80 1XP, 1 ,80 1XPHC) Heating & Cooling Equipment, Categories 169 & 294, No 236-M90 Tested thru ETL and ETLc Testing Laboratories, Report # 532015 Applies to models AHP- (1,200, 1,201, 1,200HC, 1,201HC, 1,200X, 1,200XHC, 1 ,80 1, 1 ,80 1X, 1 ,80 1XHC, 1 ,80 1HC) Reliability and mean time between failure (MTBF) The life expectancy of... Mil-Spec finishes on exterior They are designed to maintain enclosure rating and perform in the rated environment Military Standards Mil-Std 81 0 Corrosion (Salt Fog Testing) Method 509.2, 1 68 Hours, Employed for all NEMA-4X units Vibration Method 514.3, 2 hours, x, y, z axis 8. 9 G’s, 10–2,000 Hz with a magnitude of 0.04 G2/Hz, Employed for all XM- Versions, Standard models are designed to withstand 2.2 G’s... TECA.) C-417 C-4 18 Cooling; Cool, Products That (Air Conditioners); Liquid-Cooled Air Conditioners ethylene, or gases or vapors of equivalent hazard, acetone, ammonia, benzene, butane cyclopropane, ethanol, gasoline, hexane, methanol, methane, natural gas, naphtha, propane, or gases or vapors of equivalent hazard [Note: Applies to this OEM’s models AHP- (1,200XP, 1,200XPHC, 1 ,80 1XP, 1 ,80 1XPHC)] UL/CSA... to 900 cows) Milk temperature is lowered from 98 to 38 F The standard coolers available worked well in competitive dairies in the rest of the United States, as the ambient temperatures there do not impose as much of a heat load as in Hawaii Milk typically takes 2 h to cool in a large modern industrial dairy A standard air conditioner was fitted with an 80 0-gal glycol tank The milk was found to cool... industry uses a solid-state liquid chiller to precisely control fluid temperatures for water-jacketed columns and etch baths (Source: TECA.) FIG C-4 48 A manufacturing specialist of transport equipment uses a solid-state cooling system to protect electronic equipment from harsh, high-stress conditions (Source: TECA.) The design of the heat exchanger is a very important aspect of a good thermoelectric system... Figures C-4 38 through Cooling Towers C-423 FIG C-449 (Source: TECA.) C-441 provide selection options based on ambient temperature Note that model designations in these figures are specific to this information source When looking at other original equipment manufacturers’ products, look for equivalent or close to equivalent capacities Cooling Towers (see also Fans, Centrifugal) Cooling towers cool process. .. 60million-gal/day desalination plant at Jebel Ali The plant’s eight MSF units are part of a cogeneration power facility The fresh water would have been at least as much incentive in the Middle East as the increased total thermal efficiency The desalination equipment in both cases was supplied by Weir Westgarth (WW) WW designed the MSF process The principle of the system is simple: Water and steam in a closed... points Both processes may be used for purification or separation A typical example of distillation is extracting pure solvent (such as water) from a mixture of solute and solvent (such as brine) A typical example of fractional distillation is in the separation of various hydrocarbons, for instance, butane, pentane from a hydrocarbon mixture that results from some process in the overall refining process In... power-transmission equipment The simplest form of power transmission is a belt drive A belt drive can have a flat, V-belt, ribbed belt, or toothed belt design These drives are common in applications such as conveyors Conveyor manufacturers should be consulted for their catalogues on power-transmission capability D-4 Drum; Knock-Out Drum; Knock-Out Vessel In modern process industry, drive equipment might... costs ᭿ Long process cycles ᭿ ᭿ ᭿ * Source: ARCO Chemical, USA Drying D-5 Perhaps most important, freeze drying with water is restricted to those materials that are soluble and stable in a water system Much attention has been devoted to optimizing freeze-drying cycles Recent studies have shown that addition of tertiary butyl alcohol (TBA) can markedly improve the freeze-drying process TBA as a processing . 532015 Applies to models AHP- (1,200, 1,201, 1,200HC, 1,201HC, 1,200X, 1,200XHC, 1 ,80 1, 1 ,80 1X, 1 ,80 1XHC, 1 ,80 1HC) Reliability and mean time between failure (MTBF) The life expectancy of a thermoelectric. general categories that are shown in Table C-34 are material handling, food processing, industrial processing, and presses for particle boards, plastics, and rubber. Table C-34 also indicates the four. environment. Military Standards Mil-Std 81 0 Corrosion (Salt Fog Testing) Method 509.2, 1 68 Hours, Employed for all NEMA-4X units Vibration Method 514.3, 2 hours, x, y, z axis 8. 9 G’s, 10–2,000 Hz with a