Improve Energy Efficiency Using Expanders Expanders Can Take Advantage of Pressure Reductions to Drive Rotating Machines

Home , Turboexpander

Cover Story Improve Energy Efficiency Using Expanders Expanders can take advantage of pressure reductions to drive rotating machines. Information on how to assess the potential benefits of installing expanders is provided here

Sebastiano ften in the Giardinella chemical pro- Ecotek Engineering USA cess indus- Edwin Diaz tries (CPI), “a Ecotek Investments Inc. O considerable amount Freddie Sarhan of energy is wasted in and Scott pressure control valves, Sakakura where high-pressure Sapphire Technologies fluids must undergo a pressure reduction” [1]. Depending on various technical and economic IN BRIEF factors, it may be fea- EXPANDER TYPES sible to transform this energy into rotational COMPONENTS mechanical energy that Sapphire Technologies EXPANDER PROCESS can be used to drive FIGURE 1. This image shows a three-dimensional rendering of an inline turboexpander ARRANGEMENT an electrical generator or another rotating EXPANDER PROCESS DESIGN machine. In the case of best-known type of expander (Figure 1), incompressible fluids (liquids), this is accom- there are other types suitable for different EXAMPLES plished by using hydraulic power-recovery process conditions. This article describes CONCLUDING REMARKS turbines (HPRTs; explained in Ref. 1). For the main types of expanders and their com- compressible fluids (gases), expanders are ponents, and summarizes how operations the appropriate machine. managers, consultants or energy auditors in Expanders are a mature technology with various sectors of the CPI can assess the a host of successful applications, such as potential economic and environmental ben- Containment system VSDIN for fluid catalytic cracking (FCC), refrigera- efits of an expander installation. contamination-free and safe drying tion, natural-gas city gate-valve stations, air separation or off-gas venting, to name Expander types of HAPI products a few. Basically, any gas stream subject to There are many different types of expanders, Vacuum drying oven VSD with customized a pressure reduction can be used to drive varying widely in geometry and capability. isolator integration and mobile pressure nutsch an expander, yet “the energy output is pro- The main types are shown in Figure 2, with a System features portional to pressure ratio, temperature and brief description of each given below. Further • GMP-compliant design flowrate of the stream” [2], and the technical details and a chart comparing the operating • Protection of the operator or the product and economic feasibility of implementing regimes of each of these types as a function • Main and lock chamber as well as RTPs for loading and expanders in a process depends on these of specific diameter and specific speed can unloading of the product and other factors, such as the local price of be found in Ref. 3. • Scales and ﬁlter millls integrated in the isolator energy and the availability of suitable ma- Piston turboexpander. Piston and rotary- Options chines from manufacturers. piston turboexpanders operate like back- • Drying oven VSD and pressure nutsch made of Hastelloy While turboexpanders (which function in ward combustion engines, taking high- • Wall installation a manner similar to that of turbines) are the pressure gas and converting its stored • Explosion protected version (ATEX)

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12_CHE_0421_CS_Expanders_SCJ_p28-39.indd 28 3/22/21 11:42 AM Sebastiano Giardella energy into rotational energy through a Turboexpander generators can crank shaft. be configured with a direct-drive Drag turboexpander. Drag turboex- shaft from the turbine wheel to panders consist of a concentric flow cav- the electric generator or through a ity with scoop-shaped fins fixed to the gearbox, which effectively reduces periphery of the rotating element. These the input speed from the turbine are designed much like a water wheel, wheel to the generator through but the concentric cavity gradually in- a gear ratio. Direct-drive turbo- creases in cross section from inlet to out- expanders are superior in terms let, allowing for expansion of the gas. of efficiency, footprint and main- Radial turboexpander. Radial turboex- tenance costs. Gearbox turbo- panders are designed with axial-flow in- expanders are much heavier and FIGURE 2. Different types of expanders vary widely lets and radial-flow outlets, such that the require a larger physical footprint, in their geometries and their capabilities gas is expanded radially through the tur- auxiliary oil lubrication equipment bine wheel. Similarly, axial-flow turbines and regular maintenance. expand gas through the turbine wheel, Flow-through turboexpanders can be but the direction of flow remains parallel designed with radial or axial turbines. with the axis of rotation. Radial flow-through expanders contain The main focus in this article is on ra- an axial inlet and a radial outlet such dial and axial turboexpanders, discuss- that the gas flow exits the turbine radially ing their various subtypes, components from the axis of rotation. Axial flow tur- and economic benefits. bines allow the gas to flow axially along Turboexpanders recover energy from the axis of rotation. Axial turbines extract high-pressure gas streams and con- energy from the gas flow via inlet guide vert the energy to drive a load. Gener- vanes to the expander wheel, while the ally, the load is either a shaft-coupled cross-sectional area of the expansion compressor or an electric generator. chamber gradually increases to maintain Compressor-loaded turboexpanders constant velocity. compress a fluid in other parts of the process stream requiring a compressed Components fluid, and thus increase the overall plant A turboexpander generator has three pri- efficiency by utilizing otherwise wasted mary components: turbine wheel, spe- energy. Generator-loaded turboex- cialized bearings and generator. panders convert the energy into elec- Turbine wheels. The turbine wheels tricity, which can be used in other plant are typically designed specifically for the processes or returned to the local elec- application, in order to optimize aerody- trical grid for sale. namic efficiency. Application variables

Containment system VSDIN for contamination-free and safe drying of HAPI products Vacuum drying oven VSD with customized isolator integration and mobile pressure nutsch System features • GMP-compliant design • Protection of the operator or the product • Main and lock chamber as well as RTPs for loading and unloading of the product • Scales and ﬁlter millls integrated in the isolator Options • Drying oven VSD and pressure nutsch made of Hastelloy • Wall installation • Explosion protected version (ATEX) For details visit adlinks.chemengonline.com/80068-28 PINK GmbH Thermosysteme · Am Kessler 6 · 97877 Wertheim · Germany · T +49 (0) 93 42 919-0 · [email protected] · www.pink.de

12_CHE_0421_CS_Expanders_SCJ_p28-39.indd 29 3/22/21 11:42 AM Sebastiano Giardella through an electromagnetic generator, which can be either an induction or permanent magnet (PM) generator. In- duction generators are rated for lower speed, and thus require gearboxes for high-speed turbine applications, but are capable of being designed to match the frequency of the grid, thereby eliminating the need for a variable frequency drive (VFD) to transfer the generated electricity. PM generators, on the other hand, can be directly shaft-coupled to the turbine, and can deliver electricity to the grid via a VFD. The generator can be designed to output the maximum amount of electricity according to the available shaft power of the system. FIGURE 3. The diagram shows an example of an overall process arrangement for an expander generator Seals. Sealing is also a critical component in designing a turboexpander affecting turbine wheel design include system. To maintain high efficiency and inlet/outlet pressure, inlet/outlet tem- meet environmental standards, sys- perature, amount of volumetric flow and tems must be sealed to prevent poten- fluid characteristics. Turboexpanders tial process gas leaks. Turboexpanders with several turbine wheels are required can be designed with dynamic or static when the pressure ratio is too large to seals. Dynamic seals, such as labyrinth reduce via a single stage. Both radial seals and dry gas seals, provide seal- and axial turbine wheels can be de- ing around the rotating shaft, usually signed with multiple stages, but the axial between the turbine wheel and the rest turbine wheel has a much shorter axial of the machine where the bearings and length and thus is more compact. A ra- generator are located. Dynamic seals dial multi-stage turbine requires the gas wear over time and require regular to flow from axial to radial, then back to maintenance and inspection to ensure axial again, and thus produces higher they are working properly. Static seals friction losses than the axial turbine. may be used when all components of Bearings. Bearing design is critical for the turboexpander are contained inside SMART TRANSFER SOLUTIONS efficient turboexpander performance. one housing, protecting any lead wires Bearing types associated with turbo- exiting the housing, including leads for FOR CHEMICALS. expander designs vary widely and can generators, magnetic bearing actua- include oil lubrication, fluid film, conven- tors or sensors. These hermetic seals + tional ball and magnetic. Each has its provide permanent protection against + own advantages and disadvantages, as gas leaks and do not require any main- summarized in Table 1. tenance or servicing. + NEW: Vibratory feeder Many turboexpander manufacturers are transitioning to magnetic bearings Expander process arrangement + as the “bearing of choice,” due to their From a process point of view, the basic distinct advantages. Magnetic bearings requirements for an expander installa- provide frictionless operation for the tion are a high-pressure compressible dynamic components of the turboex- (non-condensable) gas being delivered pander, dramatically reducing operating to a lower-pressure system at a suffi- and maintenances costs over the life of cient flowrate, a pressure differential and the machine. They are also designed to a use factor to maintain the equipment’s adapt to a wide range of axial and radial working parameters within safe and ef- loads and surge conditions. Their higher ficient levels. upfront costs are offset by much lower From a pressure-reduction function, lifecycle costs. expanders can be used to replace a Generator. The generator takes the ro- Joule-Thomson (J-T) valve, also known tational energy from the turbine and con- as a throttling valve. Given that the verts the energy into useable electricity J-T valve follows an isenthalpic path, www.coperion.com/components 30 CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM APRIL 2021

12_CHE_0421_CS_Expanders_SCJ_p28-39.indd 30 3/22/21 11:42 AM whereas the expander follows a nearly a J-T valve is shown in TABLE 1. BEARING TYPES FOR TURBOEXPANDERS Fluid isentropic path, the latter reduces the Figure 3. Category Ball Air Magnetic Film gas enthalpy, with the enthalpy differ- In other process Adaptive to variable loads ✔ ence being transformed to shaft power, configurations, the High speed applications ✔ ✔ achieving a lower outlet temperature energy recovered in High stiffness ✔ ✔ ✔ than the J-T valve. This is useful in cryo- the expander can be Low cost ✔ genic processes aiming to reduce the directly transferred to Low parasitic load ✔ ✔ temperature of the gas. a compressor. These Maintenance Free Operation ✔ ✔ In cases where there is a lower limit to machines, sometimes the outlet-gas temperature (for example, referred to as “com- Minimal wear ✔ ✔ ✔ in pressure letdown stations, where the panders,” typically Moisture tolerance ✔ ✔ temperature of the gas must remain have the expander and No auxiliary pumps/compressors ✔ ✔ above freezing, hydrate-formation or compression stages minimum design-material temperature), linked via one or mul- No rotor contact/friction ✔ ✔ ✔ at least one heater is added to con- tiple shafts, which may Particulate tolerance ✔ trol the gas temperature. When a pre- also include a gearbox Used in process fluid stream ✔ ✔ heater is located ahead of the expander to adjust for speed inlet, part of the energy supplied to the differences between gas is also recovered in the expander, both stages. It may also include an ad- thus increasing its power output. In ditional motor to supply more power to some configurations where outlet tem- the compression stage. perature control is essential, a second Described below are some of the post-heater can be installed after the most important components that en- expander to ensure a faster control. sure the proper operation and stability A simplified diagram of the overall pro- of the system. cess arrangement for an expander gen- Bypass or pressure-reduction valve. erator with a preheater used to replace A bypass valve allows service continu-

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3854912_CHE_0421_CS_Expanders_SCJ_p28-39.indd CPC Ad for April Mag.indd 1 32 3/22/213/10/21 11:42 4:24 PMAM ation when the turboexpander is taken of the upstream flow to maintain the out of service (for example, to perform temperature of the gas at the expander maintenance or during an emergency), discharge above minimum values. The whereas a pressure-reduction valve is temperature increase has the added used in continuous operation to deliver benefit of increasing power output while excess gas, when the total flow exceeds also avoiding corrosion, condensates the expander design capacity. or hydrates that can have a detrimental Emergency shutdown (ESD) valve. An effect on the nozzle of the equipment. ESD valve is used to stop gas flowing In systems containing heat exchangers The Only Event Covering Digitalization into the expander during a contingency (such as the one shown in Figure 3), to prevent mechanical damage. gas temperature is typically controlled Instruments and controls. Important by regulating the flow of heating fluid to for the Power Generation and variables to monitor include inlet and the preheater. In some designs, a fired discharge pressures, flowrate, rotational or electric heater may be used instead Chemical Process Industries. speed and power output. of a heat exchanger. In existing J-T Overspeed trip. This device shuts off valve stations, a preheater may already the flow to the turbine, which causes the exist, and the addition of an expander turbine rotor to decelerate, protecting may not require further preheaters to Aug 30-Sep 2, 2021 • Austin, TX the equipment from an excessive speed be installed, but rather an increase in derived from unexpected process condi- heating-fluid flowrate. tions that could damage the equipment. Lube oil and seal gas systems. As de- Pressure safety valve (PSV). A PSV is scribed above, expanders may use dif- usually installed downstream of the tur- ferent seal designs, which may require boexpander to protect the low-pressure lube oil and seal gas. Where applicable, Experience the dynamic world of artiﬁcial intelligence line and the equipment. The PSV must the lube oil must be maintained at high and machine-learning to the enabling technologies be sized for the worst contingency, with quality and purity as it encounters pro- typical cases including bypass valve fail- cess gas, and the viscosity levels of the driving advanced connectivity and data analytics. ure open. In cases where the expander oil must be maintained within the required is added to an existing pressure let- operation ranges of the oil bearings. A down station, the process design team seal gas system generally accompanies should determine if the existing PSV al- a lube oil installation to prevent the oil Hosted by: ready provides adequate protection. from the bearing housing from entering Preheater. A preheater compensates the expander housing. In the particular for the temperature decrease caused by case of companders for use in the hy- passing gas through the turbine, mak- drocarbons industry, it is common to de- ing it necessary to preheat the gas. Its sign lube oil and seal gas systems to API main role is to increase the temperature 617 [5] Part 4 specifications.

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38549 CPC Ad for April Mag.indd 1 3/10/21 4:24 PM 12_CHE_0421_CS_Expanders_SCJ_p28-39.indd 33 3/22/21 11:43 AM Variable frequency drive (VFD). When rate, inlet temperature) the generator is asynchronous, a VFD • Fluid properties (including gas com- is typically included to adjust the alter- position, molecular weight, viscos- nating current (a.c.) signal to match the ity, specific heats ratio, dewpoint, frequency of the grid. Typically, designs presence of corrosive or condens- that rely on VFDs have higher overall able components) efficiencies than those with gearboxes • Design conditions (inlet and outlet de- or other mechanical components. Sys- sign pressure, design temperature tems based on VFDs also can accom- and rating) modate a wider range of process varia- • Site and utility data (location, eleva- tions that may result in varying expander tion, atmospheric conditions, utility shaft speeds. conditions, such as electricity, cool- Gearbox. In some expander designs, a ing fluid, instrument air or steam or gearbox is used to reduce the rotational heating fluid). Where multiple oper- speed of the expander to match the ating cases are foreseen, process generator’s nominal rotational speed. engineers should clearly identify The use of a gearbox comes at the ex- these cases, as well as extremes of pense of a reduction in overall efficiency, process parameters (for example, and hence output electrical power. minimum and maximum inlet pressure) and provide process data Expander process design for each. They may also provide a When preparing a request for quotation sketch of the proposed facilities, (RFQ) for an expander, process engi- such as a process flow diagram neers must first define the service condi- (PFD) or piping and instrumentation tions, including the following information: diagram (P&ID) • Operating conditions (inlet and outlet Mechanical engineers typically com- pressure, differential pressure, flow- plete the expander generator data

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12_CHE_0421_CS_Expanders_SCJ_p28-39.indd 34 3/22/21 11:43 AM sheets and specifications with the in- recommended to perform a cash- puts from other engineering disciplines. flow or lifecycle-cost analysis to These inputs may include the following: compare long-term project eco- • Design code requirements nomic performance and return • Electrical area classification on investment. For instance, a • Electrical and instrumentation higher initial investment can be requirements compensated in the long run by • Civil/structural design with seismic better performance or by reduced and wind design data maintenance requirements. For The specifications should also in- guidance on this type of analysis, clude a list of documents and drawings see Ref. 4. to be supplied by the manufacturer as part of the bidding process and as part Calculating power potential of the scope of supply, along with test All turboexpander generator ap- procedures, as applicable, according plications require an initial cal- to project requirements. culation of total power potential Technical information to be provided to determine the total amount of by the manufacturer as part of the bid- available energy that can pos- ding process should typically include the sibly be recovered in a specific AWORLD following items: application. For turboexpander • Predicted performance (hydraulic generators, the power potential LEADERIN power, power output at generator is calculated as an isentropic CHEMICAL terminals, outlet gas conditions) at (constant entropy) process. This each specified case is an ideal thermodynamic case SOLIDIFICATION • Performance curves, utility require- considering a frictionless, revers- ments and auxiliary electrical con- ible adiabatic process, but it is AND sumption the proper process for estimating • Preliminary drawings realistic power potential. HANDLING • Technical description Power potential is dependent • Scope of supply on the following input parameters: SOLUTIONS • A list of spare parts • Gas composition • A list of engineering deliverables to be • Inlet pressure, kPa-gage supplied and warranties • Exit pressure, kPa-gage Granulation, solidification and If any aspects of the proposal differ • Inlet temperature, °C handling systems for different from the original specifications, then the • Normalized volumetric flowrate kinds of chemicals like resins, manufacturer should also provide a list (0°C and 1 atm), Nm3⁄h waxes, hot melts, antioxidants of deviations along with the reasons for The isentropic power potential and stabilisers. the deviations. (IPP) is calculated by taking the The project design team, upon re- difference between the specific • High productivity – ceipt of the proposals, must then check enthalpy between the inlet and on-stream factor of 96% compliance with the RFQ, and deter- exit of the turboexpander, and • Proven Rotoform technology – mine whether any deviations are techni- multiplying the result by the mass 2000 systems installed in cally justifiable. flowrate. This power potential will 30+ years Other technical considerations that be expressed as an isentropic • Complete process lines or should be taken into account when eval- value (Equation (1)): retrofit of existing equipment uating proposals include the following: • Global service / spare parts supply • Space and utility requirements IPP = (hinlet – h(i,e)) × ṁ x ŋ (1) • Warranties offered • Lead times Where, h represents the spe- Read more at (i,e) ipco.com/applications • Operational limits cific enthalpy, considering isen- • Technical support and remote moni- tropic exit temperature, and ṁ is toring capabilities mass flowrate. • Past performance Although the isentropic power • Maintenance requirements potential is useful in estimating • Other criteria as valued by the project power potential, all real-world team systems contain friction, heat and Finally, an economic analysis should other auxiliary energy losses. Thus, be performed. Since different options a realistic power potential calcula- may present different initial costs, it is tion should consider the following For details visit adlinks.chemengonline.com/80068-18

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12_CHE_0421_CS_Expanders_SCJ_p28-39.indd 35 3/22/21 11:43 AM additional inputs: ciency can vary widely depending on the • Desired exit temperature, °C technology being used. For example, a • Total turboexpander system effi- turboexpander that utilizes a step-down ciency, % gearbox to transmit rotational energy In most turboexpander applications, from the turbine to generator will expe- the temperature is limited to a minimum rience far greater friction losses than a value to prevent unwanted issues, such system that uses a direct drive from the as freezing pipelines, as mentioned pre- turbine to the generator. Total turboex- viously. In the case of natural gas flow, pander system efficiency is expressed hydrates are almost always present, as a percentage and is considered when which means the pipes downstream estimating actual turboexpander power from a turboexpander or J-T valve will potential. The realistic power potential freeze internally and externally if the exit (PP) calculation is as follows: temperature drops below 0°C. Freezing causes restrictions in flow and eventually PP = (hinlet – hexit) × ṁ x ŋ (2) downtime to defrost. Thus, a “desired” exit temperature is used to calculate a Where: more realistic power potential scenario. h(i,e) = specific enthalpy, considering is- However, for gases such as hydrogen, entropic exit temperature temperature limitation is much lower be- ṁ = mass flowrate cause hydrogen does not change phase ŋ = turboexpander system efficiency from gas to liquid until it reaches cryogenic temperatures (–253°C). Specific Example 1: Natural gas PP calc. enthalpy is calculated using this desired Let’s consider a natural-gas pressure exit temperature. let-down application. Company ABC Turboexpander system efficiency runs and maintains a pressure let-down must also be considered. System effi- station that delivers gas from a main

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12_CHE_0421_CS_Expanders_SCJ_p28-39.indd 36 3/22/21 11:45 AM pipeline and distributes the gas to a development of a H2 infrastructure local municipality. At this station, inlet is rapidly growing. As with natu- gas pressure is 40 bar, while the exit ral gas, H2 pressure is transmitted pressure is 8 bar. The inlet temper- at high pressures and let down at ature of the gas with pre-heating is specific locations for production, 35°C, and the gas is pre-heated to storage and consumption. The dis- prevent freezing pipelines. Thus, the tinct pressure let-down cases for exit temperature of the gas should be H2 are the cryogenic liquefaction controlled such that it will not drop process from liquid transportation below 0°C. In this example, we will to gas storage, from gas storage use 5°C as a minimum exit temper- to gas distribution and from gas ature to add a factor of safety. The distribution and local transporta- normalized volumetric flowrate of tion to consumption. During the 3 the gas is 50,000 Nm /h. To calcu- hydrogen liquefaction process, H2 late power potential, we will assume is compressed and cooled to its all the gas flows through the turbo- inversion point, where the tempera- expander and calculate a maximum ture is further reduced while the gas power output. The following calcula- expands to finally reach its liquefaction is made to estimate the total out- tion temperature of –253°C. This put power potential: liquefaction process allows efficient, Natural gas mixture: high density transportation of H2 • Methane: 95.1% throughout its infrastructure. • Nitrogen: 0.1% Consider a H2 fueling station ex- • CO2: 2.5% ample where gaseous H2 is trans- SPECIALISTS IN • Ethane: 3.3% ferred from a fuel tanker to a stor- • Propane: 0.6% age tank. In this case, hydrogen’s SLUDGE DRYING • Isobutane: 0.1% storage pressure in the tanker • Butane: 0.1% is 275 bar with a temperature of • Inlet pressure: 40 bar (4,000 kPa- 60°C. The storage tank required gage) pressure is 18 bar. The gaseous › Sewage sludges • Exit pressure: 8 bar (800 kPa-gage) H2 is dispensed into the filling sta- • Inlet temperature: 35 °C tion storage tank at a rate of 5,000 › Industrial sludges • Exit temperature: 5 °C Nm3/h. The trailer is emptied in 3.5 • Normalized volumetric flowrate (0°C hours, with a turboexpander op- › Paint sludges and 1 atm): 50,000 Nm3⁄h erating during the first half of this • Turboexpander system efficiency: timeframe, while a compressor op- › Tar sludges 93% erates during the second half. The power potential available in this • Process fluid: gaseous H2 › Salts case is 342 kW at 5°C. The isentropic • Inlet pressure: 275 bar (27,500 power potential is 1,754 kW, which in- kPa-gage) dicates that further optimization may • Exit pressure: 18 bar (1,800 kPa- be considered. Further optimization gage) may include increasing the tempera- • Inlet temperature: 60°C ture of the inlet gas stream by provid- • Exit temperature: not critical ing additional pre-heating. Doing so • Normalized volumetric flowrate will increase the amount of recover- (0°C and 1 atm): 5,000 Nm3⁄h able energy from the stream, but it • Turboexpander system efficiency only makes sense if the spark spread 93% is significant enough for a beneficial The power potential available from Join us at economic case. The spark spread is Equation (2) is 318 kW and would the difference between the wholesale be dispensed into the storage tank digital ACHEMA Pulse price of electricity and its cost of pro- at a temperature of –124°C. In this duction using natural gas. case, the power produced would 15-16 June, 2021 be returned to the electrical grid or Example 2: H2 PP calculation to provide supply for the immediate Register at achema.de/en Another applicable gas for turboex- facility. During the second half of the For details visit adlinks.chemengonline.com/80068-08 panders is H2. With the global energy emptying process, the compressor industry looking more at hydrogen as will be activated to fully dispense www.sms-vt.com a long-term clean-energy solution, the hydrogen from the tanker. This Buss-SMS-Canzler GmbH Kaiserstr. 13-15 ▪ 35510 Butzbach ▪ Germany 37 CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM APRIL 2021 Phone +49 6033 85-0 ▪ [email protected]

12_CHE_0421_CS_Expanders_SCJ_p28-39.indd 37 3/22/21 11:45 AM case is an example of a net-zero pro- to use a turboexpander must include a cess. Using a turboexpander, we can re- financial component of the equation as cover energy losses and offset electrical well. Installation of a turboexpander is requirements and CO2 emissions. a capital expenditure (CAPEX), so the payback period should be carefully Example 3: Economic case evaluated to ensure the CAPEX makes Recovery of lost energy through tur- financial sense. There may also be po- boexpanders is beneficial to overall tential government incentives for offset plant efficiency, and it offsets electrical of CO2 emissions and sale of electric- requirements and reduces CO2 emis- ity to the grid. These variables are the sions, but decisions on whether or not building blocks for a valuable economic case for a turboexpander. To build a simple and straightforward economic case, the following inputs and outputs should be considered: Inputs: • Technical specifications (pressures, temperatures, flowrate and so on) • System purchase price • System installation price • Wholesale price of electricity • Price of natural gas (for pre-heating in natural gas PLD) • Plant capacity factor (what percentage of a day does the plant run?) Outputs: • Payback period • Electricity produced • CO2 emissions offset • Annual revenue Using the natural gas example from company ABC (Example 1), we can build an economic case for the purchase and installation of a turboexpander. First, we look for market availability of a turboexpander with the appropriate power production for our application. In this example, we will use a 280-kW turboexpander. The price for this system is $300,000 and the installation costs are $50,000. The wholesale price of electricity for the region where this plant is located is $0.16/kWh, while the price of natural gas for pre-heating is $0.06/kWh, bringing the spark spread to $0.10/ kWh. The plant operates about 20 hours per day, which we will round to 85% of the day, with an average flowrate of 50,000 Nm3/h. We will need to optimize the flow through the turboexpander to achieve maximum power production. Since there is 342 kW of available power, we will divert 41,000 Nm3/h of flow through the turbo-expander, while the remaining 9,000 Nm3/h flows through the pressure-reduction valve. Based on the power production For details visit adlinks.chemengonline.com/80068-25

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12_CHE_0421_CS_Expanders_SCJ_p28-39.indd 38 3/22/21 11:46 AM and wholesale price of electricity, Authors we will generate a total of $334,000 Sebastiano Giardinella is the Freddie Sarhan is the CEO of per year of electrical revenue. The vice president and co-owner of the Sapphire Technologies (16323 Ecotek group of companies (Bldg. Shoemaker Ave., Cerritos, CA cost for pre-heating the gas from 239, 3rd floor, City of Knowledge, 90703; Phone +1-562-293- 20°C to 35°C is $175,000 per Panama City, Panama / Coral Ga- 1361; Email: fsarhan@ year. Subtracting the two, we get bles, FL, USA; Phone: +507-646- sapphiretechnologies.com). He has 10311; Email: sgiardinella@ over 20 years of experience in the a net revenue after pre-heating of ecotekgrp.com). He has experience energy and aviation sectors. He $159,000 per year. To calculate in feasibility studies, corporate was formerly the vice president of management, project management business development for Cal- the payback period, we divide the and process engineering consulting in projects for the netix Technologies. Before joining Calnetix, Sarhan was CAPEX ($350,000) by the net rev- chemical and energy industries. He is a project manage- the vice president of Americas for Praxair Surface enue, yielding a payback period of ment professional (PMP), has a M.Sc. in renewable en- Technologies, in charge of all company operational and ergy development from Heriot-Watt University, a Master’s sales activities for North and South America. Prior to 2.2 years. This amounts to quite an Degree in project management from Universidad Latina that, he held the position of vice president of customer expeditious payback period for a de Panamá, and a degree in chemical engineering from service at Capstone Turbine Corp. He began his career capital expenditure. Universidad Simón Bolívar. He has written technical pub- at Rolls-Royce as a member of the industrial gas tur- lications for magazines and other international associa- bine development team. The annual electricity produced tions, and holds one patent for an energy storage system can be calculated by multiplying and method. the kilowatt-electric produced by Scott Sakakura is a sales engi- the number of hours per day times neer at Sapphire Technologies the number of days per year. We Edwin Diaz is a Mechanical Engi- (same address as above; Phone neer at Ecotek (same address as +1-562-293-1696; Email: get about 2.0 Gigawatt-hours of above; Phone: +507-203-8490; ssakakura@sapphiretechnologies. power production per year, which Email: [email protected]). com). He has eight years of experi- is equivalent to 1,000 tons of CO He has experience in the concep- ence in the energy and oil and gas 2 tual design and rating of heat ex- sectors. Previously, he was a sales emissions offset per year [5]. changers, hydraulic calculations engineer and project engineer for for conceptual, basic and detailed Calnetix Technologies, responsi- engineering projects, and support ble for managing the development of new motor/gen- Concluding remarks of the process engineering de- erator systems. Before Joining Calnetix, he was lead Turboexpander generators are a partment. He is a mechanical engineer from Florida engineer at Black Gold Pump and Supply and was re- mature technology and an ideal State University and is currently pursuing his master’s sponsible for rod pump and ESP product development. degree in mechanical engineering at the University of Sakakura holds a B.S.M.E. from California State Uni- candidate for gaseous pressure South Florida (Tampa). versity, Long Beach. let-down (PLD) applications. Tur- boexpander generator design has become more efficient and cost- effective through the integration of magnetic bearings, permanent- magnet motors and variable-speed drives. As global energy demand continues to increase, it is impera- tive for plant processes to be opti- mally efficient. Recovering lost energy from PLDs can reduce CO2 emissions, increase overall plant efficiency, offset electrical costs and generate additional revenues. ■ Edited by Scott Jenkins

References 1. Giardinella, S., Chung, K., López, D., and Ávila, M., Improve Energy Efficiency using Hydraulic Power Recovery Turbines, Chem. Eng., June 2017. pp. 59–63. 2. IPIECA, “Turbo-expanders,” from www.ipieca.org/resources/ energy-efficiency-solutions/power-and-heat-generation/turboexpanders/, accessed May 2020. 3. Nichols, K. E., “How to Select Turbomachinery for Your Applica- tion,” Barber Nichols Inc., 2012. 4. Giardinella, S., Baumeister, A., Baumeister, Z., Applying LCCA for Best Project Value, Chem. Eng., December 2020, pp. 32–39. 5. U.S. Energy Information Administration, www.eia.gov/tools/ faqs/faq.php?id=74&t=11#:~:text=In%202018%2C%20 total%20U.S.%20electricity,of%20CO2%20emissions%20 per%20kWh, accessed December 2020. 6. American Petroleum Institute, Axial and Centrifugal Compressors and Expander-compressors. 8th edition, 2014.

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