Process Engineering Equipment Handbook Episode 2 Part 1 pot

C-342 Control Systems; Controls FIG. C-365 Seal oil system for floating ring seals; API equivalent system. (Source: Sulzer-Burckhardt.) Control Systems; Controls C-343 FIG. C-366 Lube oil unit. (Source: Sulzer-Burckhardt.) FIG. C-367 Lube oil unit according to API 614. (Source: Sulzer-Burckhardt.) possible because of potential overspeed of the turbine after the release of the coupling. A method for protection of gas turbines against overtorque and overspeed is described below. The overspeed limitation is achieved through the incorporation of a hydrodynamic coupling, acting as a brake. A gas turbine generator set normally consists of three major mechanical components, a gas turbine, a gearbox, and a generator. These components are connected with couplings that besides transmitting the torque also must be able to cope with the misalignment and the displacement caused by the temperature gradients in the system. The generators operate at standard speeds, 1500 (1800) rpm or 3000 (3600) rpm. The gas turbine speed differs with the individual turbine design from 3600 to 20,000 rpm, typically. A gearbox that reduces speed is required in practically all generator set designs. The gear ratio can be as high as 12 times and different types of gearboxes are used. Aeroderivative gas turbines are based on aircraft engines with only minor design modifications. The lightweight design however also makes the turbines more sensitive to the overloads that can appear when there is a malfunction in the system. Fault conditions. From a power transmission point of view the drive during normal running conditions can be considered as smooth with small variations in the torque. The overtorque that can appear, and which has to be considered in designing the system, is a rare failure event. If we discount mechanical failures, the main potential source for overtorque is the generator. Electrical fault conditions in the generator can produce a large overtorque that is transmitted back to the system: the turbine, the gearbox, and the power transmission components. The electric fault possibilities are ᭿ Malsynchronization ᭿ Short circuit Both events involve torque peaks at the generator output shaft of a magnitude ten times full load torque (10¥ FLT). The peaks are of short duration and the torque is pulsating with the frequency of the generated current. Malsynchronization only gives few torque peaks while in a short circuit situation the pulsation of the torque can go on for some seconds. The nature and exact size of the torque peaks are well defined and normally known by the generator manufacturer. How the torque peaks are transmitted backward through the system is governed by the inertia and the stiffness of the components involved. The situation is complex and a dynamic analysis of the torque fault conditions is normally required for determination of the torque that reaches the gas turbine. Torque-limiting requirements. The turbine itself, which also is the most costly item, is in many cases the weakest link that has to be protected. The requirement for C-344 Control Systems; Controls FIG. C-368 Gas turbine generator set, general layout. (Source: J.M. Voith GmbH.) Control Systems; Controls C-345 limiting the torque can in many cases be difficult. As examples, both the Allison 501-KB7 and GE’s LM 6000 need protection at approximately 2–2.5 ¥ FLT in certain configurations. Compared to most other drives protected with torque-limiting couplings the relation between the requested torque limit and the FLT is unusually small. A shearpin coupling is inadequate for such applications. Basic design. The basic design principle of this OEM’s (Safeset ® ) coupling is to transmit the torque through a frictional joint in which torque capacity is controlled by hydraulic pressure. This coupling type connects a gear to a shaft in Fig. C-369. If the coupling is exposed to a higher torque than it can transmit over the frictional joint it will slip there. The relative movement of this slippage cuts a valve (shear tube) with a shear ring so the hydraulic pressure, the contact pressure, and consequently the transmitted torque drop to zero. The drop in torque occurs in a few milliseconds. This coupling has some basic advantages that has made it an appropriate solution in certain gas turbine generator set applications. ᭿ The torque limit is not influenced by high fatigue and remains practically unchanged after a large number of load cycles. The coupling will thus not release unneccesarily. ᭿ The torque limit is adjustable and can be set at low levels, i.e., 1.4–1.6¥ FLT and thereby protect components that have to operate close to their limits. ᭿ The resetting of the coupling after release is quick and reliable so the downtime of the unit is minimized. Typical applications outside of the power generation field are very highly loaded steel mill drives and pump drives in the chemical industry, where production downtime costs can be extremely high. Overspeed and overspeed limits. When a gas turbine is mechanically disconnected from the workload and inertia of the generator it will momentarily increase speed. The magnitude of the speed increase is controlled by the residual energy in the system, i.e., the amount of fuel that is available and how it progresses to flame out. The overspeeding is also controlled by the inertia that is accelerated by the residual energy. Therefore there is a significant influence based on where in the drivetrain the mechanical disconnection takes place. If the separation is made between the gearbox and the generator, the overspeeding gas turbine will have to accelerate not only its own inertia but also the inertia of the gearbox, which will result in a lower peak speed. Speed is a critical design factor for a gas turbine and any overspeeding requires certain actions depending on how much the speed is exceeded. Such actions could be: ᭿ Inspection of the turbine ᭿ Removal and complete disassembly For the operation and for reducing the hazards it is important to reduce the overspeed, and this can be done by including a hydrodynamic coupling in the drivetrain. The requirements on the turbo coupling are limited by letting the coupling rotate at speed and only react to the speed difference between gas turbine and generator. The braking torque is thus acting toward the relatively large inertia of the generator. The hydrodynamic principle. The torque transmission behavior of a hydrodynamic coupling (turbo coupling) is dependent mainly on the following factors. ᭿ Geometry: profile design, diameter d p ᭿ Operating fluid: density r, fluid level, viscosity n ᭿ Operating conditions: input speed w p , speed ratio (slip) n, acceleration The torque transmission behavior of the turbo coupling can be described with the following formula. T =l· r · d p 5 · w p 2 C-346 Control Systems; Controls FIG. C-369 Coupling basic design principle. (Coupling is a Safeset™.) 1, shaft; 2, hub; 3, hollow steel sleeve; 4, antifriction bearings (on each side); 5, seal (on each side); 6, shear ring; 7, shear tube; 8, oil charport. (Source: J.M. Voith GmbH.) Control Systems; Controls C-347 The performance coefficient, l, is dependent on fill level, speed ratio (slip), and the profile design. Typical l-slip curves for a typical OEM’s couplings with various fluid levels are shown in Fig. C-370. Two main features of the hydrodynamic coupling are the torsional separation and damping. Input and output speeds or torque fluctuations are dampened or completely separated from input to output side, depending on the frequency. These features have a positive effect in all applications in respect to the dynamic behavior of the complete system. This will result in lower stressing of component parts and reduced stimulation. Different applications require specific hydrodynamic coupling designs. For example: ᭿ Constant fill coupling: soft start of electric motors, torque limitation on the driven machine ᭿ Variable speed coupling: control of driven machine speed ᭿ Clutch-type coupling: separating driver and driven machine Specific coupling and profile designs have been developed to meet the various requirements. The residual energy in a gas turbine after the release of this coupling will result in acceleration to the turbine because of its relatively low inertia. To keep the overspeed within acceptable limits, a slipping turbo coupling can be used between the gas turbine and the generator, which has a relatively high inertia (Fig. C-371). For this application the turbo coupling must meet the following design criteria. ᭿ Rapid torque buildup with increasing slip ᭿ High availability Brake properties at high speed and acceleration. Figure C-372 shows the torque transmission of a turbo coupling versus slip for generator speeds of 3000 and 3600 rpm. FIG. C-370 Typical slip curves for various filling levels. (Source: J.M. Voith GmbH.) The development of the turbo coupling was conducted on a circuit that had good torque transmission capability at very high acceleration. Tests on the circuit design were carried out up to a slip of 16 percent and a maximum acceleration of 6000 rpm. The features of the turbo coupling unit include: ᭿ Resetting of the system after release ᭿ Self-contained unit, easily removed from the drive system Figure C-373 shows a compact design for this unit with incorporated turbo coupling. The flanged-sleeve 1 on the input side is connected via the intermediate sleeve 3 to the flanged shaft 2 on the output side. The serration connects the sleeve 3 to the output shaft. A friction joint connects the input shaft to the sleeve 3. The friction forces are generated by pressuring the hollow sleeve 4. The slipping torque can be set by varying the oil pressure in the hollow sleeve. C-348 Control Systems; Controls FIG. C-371 Gas turbine drive with Safeset ® and coupling (without gearbox). (Source: J.M. Voith GmbH.) FIG. C-372 Torque transmission of a turbo coupling (Voith VTK) versus slip. (Source: J.M. Voith GmbH.) Control Systems; Controls C-349 After reaching the maximum transmittable torque the input side will rotate relative to the output side. The relative movement (slip) is used to cut open the head of valve 6 (shear tube). The oil pressure in the hollow sleeve is released and the torque transmission is interrupted. The pump-wheel 7 of the turbo coupling is connected to the flanged sleeve (input) and the turbine wheel 8 is connected to the flanged-shaft (output). The acceleration of the gas turbine results in a speed difference between the coupling wheels that generates a torque as shown in Fig. C- 372. The torque is almost proportional to the slip. (See Fig. C-374.) FIG. C-373 Design of safety device consisting of Safeset ® coupling and turbo coupling. (Source: J.M. Voith GmbH.) FIG. C-374 Safety device after overload occurred. (Source: J.M. Voith GmbH.) This OEM’s (Safeset ® ) turbo coupling unit is designed in such a way that it can be mounted between two membrane couplings. This allows the assembly and removal of the unit without disturbing the gearbox or the gas turbine. Simulations of LM 6000 fault events. Figure C-375 shows the speed response of a LM 6000 gas turbine and generator using the torque speed characteristic (Fig. C-372) of a turbo coupling (Voith turbo size 682). The speed response without a turbo coupling is also shown. The significantly lower speed using a Safeset ® and turbo coupling can clearly be seen. The calculation assumes the following data are known. ᭿ Inertia of input side ᭿ Inertia of output side ᭿ Disconnection time of the generator ᭿ Losses in the generator (drag torque) ᭿ Torque/speed/time behavior of the gas turbine considering the acceleration Controls, of Power Supply Fluctuations and disturbances in a power supply can have expensive consequences for the process engineer. A 2-s power interruption in a semiconductor plant cost over $70,000 in 1997 dollars. The following* cases illustrate the costs associated with power fluctuations. The power behind thunderstorms can cause problems for industrial facilities where electronic systems that control critical equipment are sensitive to the storms’ slight voltage disturbances. These brief voltage sags can disrupt process electronics, resulting in losses in production and costly downtime to recalibrate and restart the C-350 Control Systems; Controls FIG. C-375 Speed response of the gas turbine and the generator with and without safety device. (Source: J.M. Voith GmbH.) *Source: Adapted from extracts from “Compensating for Lightning,” Mechanical Engineering Power, ASME, November 1997. [...]... International Power Generation, July 19 98 C-3 52 Control Systems; Controls FIG C-376 The PQ2000 system offsets voltage disturbances caused by storms, thereby preventing costly production -equipment shutdowns (Source: Mechanical Engineering Power, ASME, November 19 97.) FIG C-377 Schematic for the wearing of the PQ2000 (Source: Mechanical Engineering Power, ASME, November 19 97.) Control Systems; Controls... maintained The PQ2000 and other improvements, such as properly grounded and improved electrical drives, trimmed the Homerville factory’s annual electrical costs from a high of $11 0,000 to $ 12 0 ,000 down to $60,000 to $70,000 (see Figs C-376 and C-377) Using this system to correct a 2- s power outage can save a semiconductor manufacturing plant $70,000 in product that would otherwise be lost The same 2- s interval... system switches the load back to the utility Speed is of the essence The PQ2000 can deliver up to 2 MW in about one-quarter of a cycle (or 1 /24 0 s) to maintain power to critical equipment Most power disruptions typically last only a few cycles, so the AC Battery engineers designed the power-storage system to dispense power for up to 10 s, ensuring an extra margin of safety This system demonstrated its ability... storms’ slight voltage disturbances These brief voltage sags can disrupt process electronics, resulting in losses in production and costly downtime to recalibrate and restart the * Source: Adapted from extracts from “Compensating for Lightning,” Mechanical Engineering Power, ASME, November 19 97 Control Systems; Controls C-3 51 equipment A pilot project funded by Oglethorpe Power Corp in Tucker, Ga.,... thermocouples ᭿ DT alarm ᭿ DT shutdown ᭿ Thermocouple spread alarm ᭿ Thermocouple spread shutdown ᭿ Turbine maximum limit ᭿ Turbine minimum limit ᭿ GP speed #1 ᭿ GP speed #2 ᭿ GP speed #3 ᭿ GP speed #4 ᭿ GP speed #5 ᭿ NPT speed #1 ᭿ NPT speed #2 ᭿ TIT switch #1 ᭿ Manual ᭿ High firing fuel pressure shutdown ᭿ Transmitter failure alarms ᭿ Transmitter failure shutdowns C-357 C-358 Controls, Retrofit ᭿ ᭿ Output failure... power supply can have expensive consequences for the process engineer A 2- s power interruption in a semiconductor plant cost over $70,000 in 19 97 dollars The following* cases illustrate the costs associated with power fluctuations The power behind thunderstorms can cause problems for industrial facilities where electronic systems that control critical equipment are sensitive to the storms’ slight voltage... ᭿ Vibration system upgrade ᭿ Installation and commissioning ᭿ Training Controls, Retrofit C-359 Application case 2 The Series 9500 integrated control system provides cost-effective complete or partial control system retrofits for gas turbine–driven generator packages (see Figs C-3 81 and C-3 82) The Series 9500 system provides replacement controls for outdated electrohydraulic and analog-electronic controls... (Source: Petrotech Inc.) C-364 Controls, Retrofit 385 386 Compressor performance curves showing a 10 percent safety margin established at design ratio, and 10 percent safety margin at the highest ratio (FIG C-385) Calibration of 10 percent at design ratio results in a loss of safety as ratio increases Calibration of 10 percent at the highest ratio results in excess recycle and loss of efficiency This information... Nonproprietary interfaces: Simple 4 20 mA and dry contact I/O allow simple interface to existing or customer-implemented sequence/protection logic unit, making low-cost upgrades practical, and system troubleshooting simple Specifications ᭿ Inputs/outputs: Number of discrete inputs: 16 ᭿ Number of discrete outputs: 8 ᭿ Number of analog inputs: 24 ᭿ Number of analog outputs: 1 standard, up to 7 total ᭿ ᭿ Typical... inputs: 24 ᭿ Number of analog outputs: 1 standard, up to 7 total ᭿ ᭿ Typical electrical system: Power input: 30 W maximum, basic unit with no options ᭿ Voltage: 24 VDC nominal (18 – 32 VDC) ᭿ Relay outputs: 5 amps at 30 VDC ᭿ Analog output signals: 4 20 mA, maximum load impedance 800 ohms ᭿ Application case 4 The steam turbine compressor drive application retrofit control package (see Figs C-398 and C-399) . the PQ2000 system switches the load back to the utility. Speed is of the essence. The PQ2000 can deliver up to 2 MW in about one-quarter of a cycle (or 1 /24 0 s) to maintain power to critical equipment. . maintained. The PQ2000 and other improvements, such as properly grounded and improved electrical drives, trimmed the Homerville factory’s annual electrical costs from a high of $11 0,000 to $ 12 0 ,000 down. shutdowns. (Source: Mechanical Engineering Power, ASME, November 19 97.) FIG. C-377 Schematic for the wearing of the PQ2000. (Source: Mechanical Engineering Power, ASME, November 19 97.) Control Systems;