Gas 2024 Issue

Subcooler

Condenser

Residue gas to compression

Booster

R e f lux accum.

Residue gas to compression

Expander

Gas/gas

Booster

Cold sep.

Inlet gas

Expander

J–T valve

Reux pump

Demethaniser

Gas/gas

Cold sep.

Inlet gas

Reboiler passes

J–T valve

Deethaniser

Stagnant piping and equipment

Liquid product

Reboiler

Figure 6 Ethane recovery plant (main dryout path and stagnant areas)

Stagnant piping and equipment

Liquid product

just outside the isolation points during dryout. In this situa- tion, ensure low-point drains are installed at these locations to drain any free water that may collect during dryout. Provisions for stagnant process areas The following process flow diagrams (PFD) are examples of two typical cold plant designs: one designed for ethane recovery (see Figure 6 ) and one designed for propane recovery (see Figure 7 ). Each PFD identifies major pro - cess equipment and control valves and highlights the main recirculation flow path through the cold plant as well as the stagnant flow areas during dryout. Several piping and equipment loops and the lower sec- tion of the fractionation column below the expander outlet feed are stagnant (no dryout flow). Unless a flow is intro - duced, these areas of the cold plant will remain wet. Design provisions must be included to introduce flow into each stagnant area. A source of dryout gas is located downstream of the dehydrator dust filters (also downstream of the pressure- reducing device used for dryout), but upstream of the cold plant should be selected to provide dryout flow to each stagnant area. As an example, for a 200 million standard cubic feet per day (MMSCFD) or 5.4 x 106 normal cubic metres per hour (Nm³/hr) cold plant, a 4in minimum pipe size is recommended from the dryout gas source to provide adequate flow of dryout gas to multiple stagnant areas at once. As the cold plant nameplate capacity increases, scale up the dryout gas source pipe size accordingly to ensure adequate flow at the recommended 30 psi allowable J-T valve pressure drop during dryout. Part 2: Closed loop dryout method and monitoring UOP Ortloff has witnessed many cold plant dryouts dur - ing commissioning and initial start-up over the years. A well-conducted cold plant dryout will help plant com- missioning and ensure start-up goes smoothly and does not last longer than necessary. There are multiple dryout options which can remove water from the system, as dis- cussed in Part 1 of this two-part article. However, there are

Figure 7 Propane recovery plant (main dryout path and stagnant areas)

drawbacks to some of them. The closed-loop recirculation dryout effectively removes water from the system while easily monitoring dryout progress This allows for a quick transition to plant cooldown after dryout is completed. Some of the design challenges, the method for implement- ing a closed-loop recirculation dryout, and monitoring pro- gress will be discussed in further detail in PTQ Q2 2024. References 1 Engineering Data Book , 12th ed., Gas Processors Suppliers Association, Tulsa, OK, 2004, Section 20, pp.9. 2 Carrol J, An Introduction to Gas Hydrates , 2008, [Online] Retrieved May 13, 2010, www.telusplanet.net/public/jcarroll/HYDR.HTM. 3 Engineering Data Book , 12th ed., Gas Processors Suppliers Association, Tulsa, OK, 2004, Section 20, pp.19. 4 Engineering Data Book , 12th ed., Gas Processors Suppliers Association, Tulsa, OK, 2004, Section 20, pp.23. Scott A Miller is a Principal Process Engineer with Honeywell UOP, supporting Ortloff Cryogenic Gas Processing Technologies. He has more than 23 years of experience in the petrochemical and gas pro - cessing industries, of which 15 are in the design and operation of NGL/ LPG recovery plants. Email: scott.a.miller@honeywell.com David A Jelf is a Principal Instrument and Controls Engineer with Honeywell UOP, supporting Ortloff Cryogenic Gas Processing Technologies. He has more than 40 years of experience in the design and operation of NGL/LPG recovery plants. J A Anguiano is a former Engineering Manager with Honeywell UOP, previously supporting Ortloff Cryogenic Gas Processing Technologies. He has more than 25 years of experience in the design and operation of NGL/LPG recovery plants. Joe T Lynch is a retired Engineering and Licensing Manager from Honeywell UOP, previously supporting Ortloff Cryogenic Gas Processing Technologies. He has more than 45 years of experience in the design and operation of NGL/LPG recovery plants.

Gas 2024