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Separex™ Membrane System – Operating Manual Process Flow and Control uop No. 956457, Rev. 1 IV-1 A Honeywell Company This information is confidential and must not be used for any purpose, duplicated, or disclosed to others without UOP's written permission. IV Process Flow and Control A. PROCESS FLOW The Guara One-Stage Membrane unit consists of the major components shown in the diagram below. Typical Flow Diagram One-Stage Separex™ Membrane System The One-stage SeparexTM Membrane System can be designed to process various flow rates of feed gas with a broad CO2 content range at a design minimum feed temperature and minimum feed operating pressure. For the multiple cases of operation, the Separex Membrane System will produce sales gas from the Membranes with a maximum sales CO2 content. Membrane permeate pressure control, the number of trains brought on line, and preheaters are adjusted as the membranes flow rate, condition, and composition requires or as the membranes age. The rated feed case membrane train configurations, rates, compositions and conditions are presented in Table 1 below. For Detailed Process Flow and Control Sketches, refer to UOP’s S660M Specification. Separex™ Membrane System – Operating Manual Process Flow and Control uop No. 956457, Rev. 1 IV-2 A Honeywell Company This information is confidential and must not be used for any purpose, duplicated, or disclosed to others without UOP's written permission. B. MEMBRANE PREHEATER CONTROLS Treated gas leaving the Dew Point Control Unit (DPCU) enters the Separex Membrane System and is sent to the Membrane Preheater(s) where the gas is heated if required. Feed to the membranes is warmed by passing a fraction of the feed gas through the membrane preheaters. The membrane feed temperature is controlled by TIC-2710-02 through split range control that first opens TV-2710-02A, the heating media valve (0 to 100% opening for a controller output of 0 to 50%), and then closes TV-2710-02B, the feed bypass valve (100 to 0% opening for a controller output of 50 to 100%), to send more flow through the preheat exchangers. Manual valves (8” D-2RRC-283-007, 8” D-2RRC-283-014 and 8” D- 2RRC-283-016 on the feed gas and 3” D1H-2RRC-283-033, 3” D1H-2RRC-283- 037 and 3” D1H-2RRC-283-041 on the heating media) are closed to stop the flow through the preheat exchangers. C. MEMBRANE TRAIN CONTROLS From the Membrane Preheaters the gas is fed to the Membranes. The Membranes separate the CO2 from the feed gas to the required sales gas specification and collect in the permeate piping as controlled via a pressure controller at low pressure. As the hydrocarbon components of the feed gas permeate much slower than CO2, these components are concentrated in the high- pressure residual stream. Since the membrane is not a perfect separator, some methane will pass into the low pressure permeate stream. The permeate gas from these Membranes is sent to a CO2 Reinjection Compressor. In case this downstream compressor is not operational, the CO2-rich permeate will be flared. Each individual membrane train is capable of turn-up or turndown. Multiple trains, operated in parallel, are typically required to produce the design export gas. The trains allow for operational flexibility for a wide range of feed flow rates and compositions. As the flow rate and/or the CO2 concentration is/are increased, more membrane banks are needed on line to meet the CO2 removal requirements. Membrane maintenance activities can be performed by removing a train from service. At reduced export gas demand or the reduced feed gas rates, membrane trains can be taken out of service as needed to maintain product quality and hydrocarbon recovery. Figure 1 demonstrates the boundaries within which the unit can be operated with the feed CO2 concentration being between 8 – 35%. This figure has been generated using the design specification of the unit in keeping the desired product specifications. The number of trains (that is A, B & C) to be put online is directly related to the membrane area required (calculated as number of Separex™ Membrane System – Operating Manual Process Flow and Control uop No. 956457, Rev. 1 IV-3 A Honeywell Company This information is confidential and must not be used for any purpose, duplicated, or disclosed to others without UOP's written permission. tubes online) for the entire process. It is important to realize that each train contains varying number of tubes to allow flexibility in their individual or combined CO2 removal capacity. Trains A, B and C have 24, 36 and 48 tubes respectively. For example, if the feed gas flow rate is 3.40 MMSCMD with a CO2 concentration of 8%, then from the figure below, it can be determined that 60 tubes will be required for this particular scenario. Hence, a combination of Trains A and B will be required ideally to be put online for the unit to meet the desired product specifications. Similarly, if feed gas flow rate is 3.40 MMSCMD with a CO2 concentration of 32%, then the number of tubes required would be 84 (as the solid line passes closer to 84 tubes rather than 72 tubes) which would imply that Trains B and C will have to be online. Note that in the graph below, the feed temperature of the gas to the membranes may be different in each case. Figure 1 Each of the cases have been defined in the Table 1 in the following page. The data points without any case numbers are intermediate points generated by the simulation model in UOP. In each of these cases, the feed tempereature was 35°C and the permeate pressure was 401 kPa (a). Separex™ Membrane System – Operating Manual Process Flow and Control uop No. 956457, Rev. 1 IV-4 A Honeywell Company This information is confidential and must not be used for any purpose, duplicated, or disclosed to others without UOP's written permission. Table 1 X = online The overall system performance can be adjusted by manipulating a combination of: • Membrane permeate pressure via Pressure Control Valve on the Membrane Skid or Compressor Suction Pressure Control (Out of Scope and downstream) • Number of Membrane Trains used. • Membrane feed gas temperature. D. DISTRIBUTED CONTROL SYSTEM AND INSTRUMENTATION The Separex Membrane System is controlled by a Distributed Control System (DCS). Key controls for membrane performance are via feed temperature controls on the preheater, and permeate pressure controls, limited by the minimum suction capacity of the membrane permeate re-compressor. The Emergency Shutdown and Process Control Systems are capable of operating as stand-alone systems that initiate the shutdown and blow down of the Membrane System during upset conditions. Process upsets and shutdowns are annunciated through the DCS. The Pretreatment and Membranes Train’s Instrumentation consist of transmitters for temperature, level, flow, pressure, and analytical control. The alarm set points for the membrane system will occur when one of the alarm switch set points exceeds its preset limit. A Process Shutdown of the membrane system will occur when any one of the shutdown switch set points exceed preset limits, or can be operator initiated remotely from the control room. Both the feed temperature and the feed flow alarm settings will be discussed below to demonstrate logic used to program RATED CASE FLOWS, CONDITIONS, AND TRAIN USAGE Parameter Case 1 2 3 4 5 6 FEED Mol% CO2 8.3 11.9 18.0 20.7 35.7 30.7 FEED FLOW MMSCMD 2.81 4.43 4.47 4.67 1.44 4.73 A → 24 Tubes ; B → 36 Tubes ; C → 48 Tubes A X X X B X X X X X TRAINS ONLINEC X X X X X Separex™ Membrane System – Operating Manual Process Flow and Control uop No. 956457, Rev. 1 IV-5 A Honeywell Company This information is confidential and must not be used for any purpose, duplicated, or disclosed to others without UOP's written permission. the alarm system in the DCS. Some of the membrane train shutdown triggers will also be discussed below. 1. Feed Gas High Temperature Alarm The high temperature alarm (TAH) set point is constant at 60°C. The alarm is labeled TAH 2710-02. Refer to the S623M-1 specification. 2. Feed Gas Low Temperature Alarm The feed gas temperature alarm low (TAL) TAL-2710-02 has been set using a combination of two linear relationships with respect to the CO2 concentration in the feed gas. Two relationships exist for feeds above and below the 20% feed CO2 concentration level. Refer to the S623M-1 specification for these correlations. Figure 2 3. Feed Flow Alarm Low (FAL) The feed flow alarm low setting is based on linear behaviors generated from the simulation model as a function of the feed CO2 concentration. Figure D.3 shows two separate linear trends at 8% (lower limit of design Separex™ Membrane System – Operating Manual Process Flow and Control uop No. 956457, Rev. 1 IV-6 A Honeywell Company This information is confidential and must not be used for any purpose, duplicated, or disclosed to others without UOP's written permission. specification) and 35% (upper limit of design specification) CO2 concentration in feed. Each of these trends represents the varying combination of trains that could possibly be online at any given point of time during regular unit operations. The stars between the lines represent the low flow alarm setpoints as a function of sections online and CO2 concentration in feed. The correlations are provided in the S623M-1 specification. Figure 3 These trends will be programmed into the Local Control Panel (LCP) as a part of the logic system. However, it is important for the operator to understand that the alarm set points change with the changing CO2 concentration in the feed gas. Separex™ Membrane System – Operating Manual Process Flow and Control uop No. 956457, Rev. 1 IV-7 A Honeywell Company This information is confidential and must not be used for any purpose, duplicated, or disclosed to others without UOP's written permission. 4. Feed Flow Alarm High (FAH) The CO2 Membrane feed gas high flow alarm limit is a function of the number of membrane tubes online. Because the trains have different number of tubes, the FAH depends on which trains are online. The following table shows the FAH alarm set points as a function of the number of tubes online. Trains Online FAH (MMSCMD) A 1.6 B 2.4 C 3.2 A + B 4.0 A + C 4.9 B + C 5.7 A + B + C 5.8 The LCP will make the required alarm adjustments for the trains starting- up or online which will be manually entered by the operator using a selector switch (HS-2705-02x). The selection will be checked with the position signals from the membrane train feed valves (ZI-2705A-01, ZI- 2705B-01, and ZI-2705C-01) 5. Feed Treatment Section Emergency Shutdown An ESD of the upstream feed treatment system will result in an ESD of the membrane system as well. This prevents untreated feed gas from reaching the membranes. This ESD is outside the scope of this manual. 6. Low Membrane Feed Flow Rate Shutdown The setting for FSLL-2705-01A is a function of the CO2 content in the feed (AI-2705-01A) and the number of membrane trains online and initiates Separex™ Membrane System – Operating Manual Process Flow and Control uop No. 956457, Rev. 1 IV-8 A Honeywell Company This information is confidential and must not be used for any purpose, duplicated, or disclosed to others without UOP's written permission. a shutdown of the membrane system. See formulas in the UOP S660M Specification. 7. Low Membrane Feed Inlet Temperature Shutdown The membrane feed temperature measurement range for TI-2705-01A is from 0 to 70 °C. The setting for TSLL-2705-01A is a function of the CO2 content in the feed (AI-2705-01A) and initiates an ESD of the membrane systems. See formulas in the UOP S660M Specification. 8. High Membrane Feed Inlet Temperature Shutdown The setting for TSHH-2705-01A is 65°C and initiates an ESD of the membrane system. Refer to UOP’s S660M Specification.
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