Recently, a series of tests were performed at a Saudi Aramco refinery continuous catalyst regeneration plant (CCR) to examine compressor trip mitigation. Two recycle gas compressors operating in parallel at 50% capacity feed H2 to the CCR. Each compressor is rated for 6 MW, with a maximum continuous speed of 6,200 rpm. They enable hydrogen-rich gas circulation in the reactor circuit. A steam turbine (K-400B) and a variable frequency drive (VFD) electric motor (K-400 A) act as drivers. Each compressor had a different head, so the start-up and shutdown sequences were complicated, and required special consideration. Steam turbine tripping necessitated a total plant shut-down since it could not be restarted while the motor driven compressor was running. K-400B trips lasting longer than four hours and led to total plant shutdown or 60% capacity operation.


Uncovering design limitations of the CCR compressors during commissioning indicated major operational issues for the CCR plant. The current engineer-procure-construct (EPC) design called for a start up of the steam turbine driven compressor (K-0400B) prior to start up of the motor driven compressor feeding H

o the CCR. This wasn’t reflected in any of the process licensor or EPC documents.

During normal unit capacity, K-400B can’t start while J10-K-400A is online, as K-400B can’t develop pressure at idle speed. Upstream pressure of the J-10-E-410 (reactor effluent air cooler) would be almost 2.8 barg while K-400A is running, and lead to K-400B going into surge with the existing piping layout (Figure 1).

Figure 1: Schematic of H2 recycle gas compressors. Courtesy of Saudi Aramco.

Idling mode with 1,500 rpm is required for the compressor turbine KT-0400B prior to increasing the turbine speed to its minimum 4,200 rpm. It cannot be carried out when K-0400A is in operation, since a compressor head with 1,500 rpm is not sufficient to overcome the required discharge pressure developed by the reactor effluent and recycled gas flowing through the effluent condensers. The anti-surge spillback line is taken from the individual compressor discharge and connected upstream to reactor effluent condenser E-0410. With K-0400A running, pressure drop is created through E-0410, E- 0411A/B, and the associated piping. It was too high for K-0400B under idle, and thus, shall be lower than the achievable discharge pressure at 1,500 rpm.

 recycle gas compressor system pressure is governed by the naphtha liquid feed. Reactor circuit pressure drop and recycle gas pressure is largely determined by hydrocarbon flow, rather than compressor speed. This means while K-0400A is running, altering its speed will not influence the reactor circuit pressure drop as much as the liquid feed.


By starting K-400 B first, idling operation can be performed before increasing turbine speed. After reaching minimum turbine speed on compressor-B, compressor-A starts. Afterwards, liquid hydrocarbon is introduced to the reactor. If compressor-B is tripped for any reason, several solutions can alleviate the issue of common tie-in of the compressor’s recycle line to the effluent condenser, mitigating operational limitations.

One route involves continuing turndown operation only with compressor-A, until problems with compressor-B can be resolved. Once compressor-B is fixed, idling operation of the compressor-B turbine can commence. Next, shut down the unit by stopping the feed; then shutdown compressor-A. With intermediate storage tanks, the upstream/downstream units can continue, so impact on the aromatic production should be limited. The upstream naphtha hydro-treating (NHT) will continue to run by sending hydrotreated naphtha to the hydrotreated naphtha storage tank.

Figure 2: New line to depressurize compressor-B to flare during idling. Courtesy of Saudi Aramco.

Another is to provide a new recycle line from the compressor discharge to flare so that the compressor-B’s discharge can be depressurized to atmosphere. Hydrogen rich gas would be vented and lost to flaring (Figure 2).


A third choice is installing a new recycle line from compressor-B’s discharge to the compressor common suction before the split to the compressors. This ensures compressor-B operates independently from compressor-A during idling, as both compressors have a dedicated loop (Figure 3).

Figure 3: Proposed piping modifications to enable idling. Courtesy of Saudi Aramco.


Both the first and second options ended up being excluded. One leads to major process interruption and requires extensive effort to shut down and restart the plant. Number two extrudes high levels of hydrogen rich gas to the atmosphere.

Option three was deemed the best solution. It provided higher operational flexibility, is less harsh on the environment, and only requires minor piping modifications. To eliminate compressor-B surge during turbine idling operation, the discharge pressure of compressor-B must be depressurized and equalized to the suction pressure. This is achieved by providing a new line, bypassing the reactor effluent condensers. With low-speed idling, the temperature rise through compressor-B is marginal, and the required flow rate is small compared to the gas flow rate circulated with compressor-A. Idling operation can be done without temperature escalation at compressor-B’s discharge, as long as the discharge gas is combined with gas from the separator (compressor-A). Here, no additional spillback gas cooler is required (Figure 4).

Figure 4: Compressor performance curve at different proposed idling speed.
Courtesy of Saudi Aramco.


The differential pressure across J10‐E‐0410, J10‐E‐0411A/B and the associated piping is expected to be approximately 0.2-0.25 bar under 50 % operating load, as per a system hydraulics simulation. According to the performance curve provided by the compressor vendor, the allowable pressure differential between compressor suction and discharge in the idling mode (1,500 rpm) is limited to 0.14 ‐ 0.20 bar. Raising the idle speed was needed to meet differential pressure of 0.2 bar at 50% load. The compressor and steam turbine vendor proposed up to 2,200 rpm for idling compressor-B, which is near the critical speed of the train. This wasn’t possible, as the steam turbine would trip due to high vibration near the critical point. Pressure drop across the loop means pressure upstream the condenser will not be overcome.

Figure 5: Proposed piping modification for compressor-B.
Courtesy of Saudi Aramco.

Whenever a compressor trips, the plant operation tends to maintain maximum production from the other compressor, which can handle up to 65% of the plant’s capacity. This adds an additional required discharge pressure to be developed by compressor-B, increasing the differential pressure across E-410 and E-411 to approximately 0.3 bar. Compressor surge tends to occur during idling mode when the compressor J10‐K‐0400A is running. Figure 5 shows how this modification adds more operational flexibility, as it allows compressor-B to work independently from the other compressor during idling speed.

Plant management approved Option 3. Moving ahead, more plant flexibility is expected without the need to shut down the plant. Now, the steam turbine compressor will be reset if tripped. Although plant design undergoes several review cycles, important aspects of the design could possess greater limitations for plant operation. Special attention must be paid during dynamic simulation of the compressor anti-surge system and startup scenarios to prevent downtime costs. 

Saudi Armaco is a Saudi Arabian-based petroleum and natural gas company. Its focus is on generating value across the hydrocarbon chain through energy production, chemical refinement, carbon management, and research and development. Visit aramco.com to learn more.

Dynamic simulation of compressor anti-surge system demands special care.

Recycle Gas Compressor Challenges

Bridging the Gap With Mobile Power: The March/April 2023 Print Release

Companies in the power generation and energy sectors are adapting to recent changes in the landscape. Some segments of the market are taking them on better than others. One success story is that of LNG. Expanding infrastructure for LNG requires increased compressor optimization to handle higher volumes of gas more reliably. HRSGs, too, are in greater demand since they decrease plant energy consumption per ton of LNG produced. Onshore and nearshore LNG applications are adapting to decarbonization initiatives. These and other trends are discussed below to highlight the various ways companies are tackling challenges related to LNG production, transportation, utilization, development, and decarbonization.


Patrice Laporte, Vice President of Sales Compression Americas, Siemens Energy, outlined how the company offers high-speed reciprocating, process reciprocating, and centrifugal compressors. Driven by the shifting energy map of Europe and the Inflation Reduction Act in the U.S., the market currently sees significantly increased demand for LNG, CO2, and hydrogen. For CO2 applications, integrally geared compressors are seeing an increased need to modularize the package to reduce lead times. The hydrogen market is also picking up. Generally, the entire gas value chain is driving higher demand.

“Special attention is required for the compressor aerodynamic path design and its integration to the overall LNG plant to meet performance requirements.” said Patrice Laporte, Siemens Energy.

One of the most significant use cases for compressors is in refrigeration. For main refrigerant (MR) applications, compressors increase the pressure of the refrigerant employed to meet process conditions. Depending on the technology employed, normal operating conditions have pressures that can go approximately above 60 bar/870 psi and temperatures as low as -30 °C/-22°F. This machinery operates continuously and is the largest power consumer and operating expense contributor in an LNG plant. Special attention is required for the compressor aerodynamic path design and its integration to the overall LNG plant to meet performance requirements. 

Single shaft horizontally split compressor casings, such as the above, are suitable for boil off gas trains. Courtesy of Siemens Energy.

Boil-off-gas (BoG) involves pressurizing vapor byproduct through a compressor that is developed throughout the LNG process and storage units. For this use, LNG vaporizes through expansion and heat input with temperatures as low as -160°C/-256°F. Emissions are one of the top priorities in the conversation of plant operations.

There is debate abut using e-LNG compression trains over gas turbines to support emission reductions efforts and decarbonization solutions, particularly for onshore and nearshore LNG. Smaller-scale solutions at 2 MTPA and lower are becoming more prevalent due to faster project duration from the final investment decision (FID) to first LNG production, said Laporte. Further implementation of Voltage Source Inverters (VSI) versus Load Commutated Inverters (LCI) drives helps reduce inter-harmonics. It should be noted that power limitations of large VSI drive systems are becoming less of an issue and will soon be comparable to LCI. Variable Frequency Drive (VFD) systems allow speed control during operation and transient events. Electrical drives are advantageous as they enable independent power and speed manipulation, extending operational capabilities.


Rotoflow has a significant stake with turbomachinery utilization in LNG. The company’s ETAC high-pressure turboexpander line provides refrigeration for air separation and liquefaction facilities around the world. The expander compressor has impeller sizes of 3.5” to 22” and power from 4 to 14,000 kW. However, larger impellers and powers have been adapted. The largest impeller deployed by Rotoflow to date has a diameter greater than 50”, said Bradford Jeanes, Rotoflow Proposal Manager, New Equipment & Product Technology.

Several Rotoflow compander models have been marinized or specifically tailored for coastal or offshore applications, as seen in this FLNG facility, to withstand the harsh and corrosive saltwater environment. Courtesy of Rotoflow.

Jeanes called attention to the promise of small-scale LNG. Rotoflow’s ETAC-16R high-pressure compander products are used in a variety of LNG facilities, whether land based or floating vessel. One project currently underway is the manufacturing of a large number of high-pressure turboexpanders for an LNG producer in Qatar. Rotoflow’s compander is part of its small-scale LNG (ssLNG) peak-shaving product offering. The ETAC-7R, 8R, and 10R frame models are typically used in peak shaving applications to meet demand spikes. LNG can be seen as the balanced choice between environmental and efficiency considerations, said Jeanes. Demand for clean fuels such as LNG is high right now and for the foreseeable future, he added.

“The largest impeller deployed by Rotoflow to date has a diameter greater than 50”, said Bradford Jeanes, Rotoflow.

Other ways Rotoflow works with LNG are through its ssLNG product line. It offers nitrogen-based refrigeration cycles with an established reference base. Rotoflow is partnering with Air Products’ LNG business, providing new frame solutions (EC-30s and EC-40s) for ssLNG plants. Rotoflow sees LNG as a keystone in developing lower carbon, cleaner energy, without compromising production capabilities.


FS-Elliott offers centrifugal compressor products used in support of LNG production. Its PAP Plus compressor product line is used in LNG and similar applications, according to Dominic Sarachine, Product Manager, Engineered and Air Separation, FS-Elliott. The company’s design philosophy advocates accessibility while meeting specific industry, customer, and site requirements.

The PAP Plus compressor has a completely removable air-end and horizontally split gearcase design. Customization is one of its prime advantages. The product line provides continuous compressed air for instrument air, plant, and process air compressor applications in LNG plants. Compressor capacities start at around 1,000 cfm (35 m3/min) and reach up to 25,000 cfm (700 m3/min). Steady and reliable compressed air is needed to curtail unplanned downtime, said Sarachine. PAP Plus compressors also accommodate site-specific needs, including human factors engineering (HFE) requirements, or hazardous area requirements for operator and plant safety. Operating conditions always need to be considered. Advances in technology mandate continued evaluation of site productivity capabilities.

This compressor package for a Middle Eastern oil refinery features an instrument rack with transmitters for local monitoring and a walkway platform for maintenance access. Also included are fan-cooled air-to-air heat exchangers for cooling between compressor stages. Courtesy of FS-Elliott.

Sarachine noted that LNG plants tend to reach high operating efficiencies while working at rated conditions. These capabilities depend on practical aerodynamic and mechanical design expertise. LNG today is more focused on equipment performance across wider operating conditions when designing and operating plants, he said. This improved efficiency can contribute to emission reduction. Achieving a broader flow and pressure range while maintaining the greatest efficiency does not necessarily require new impellers, casings, or motors. Simply utilizing the latest advances in control system technology can broaden the operating range of a machine. For example, FS-Elliott’s Regulus Control System offers an energy advisor system to provide operators with recommendations on improving efficiency and a data-driven predictive maintenance module to notify when restorative actions are necessary. Web-based remote monitoring provides a look at compressor health. It’s all part of the bigger conversation on digitalization, paving the way for increasingly accurate and effective measurements.

“LNG is now focused more on equipment efficiency across wider operating conditions when designing and operating plants. This improved efficiency can contribute to emissions reduction,” said Dominic Sarachine, FS-Elliott.

Christian Brotel, Head of Sales Industries, Midstream at MAN Energy Solutions touched on the versatility of LNG in meeting new emission requirements. Some of MAN’s most popular compressor models are horizontally split (RH) or barrel-type (RB). These centrifugal compressors are used in chemicals, exploration, production, industrial gases, and more. The models cover a wide range of flow rates along with high discharge pressures. The modular configuration includes predesigned and customizable centrifugal compressor packages.

One special offering of MAN is in Factory LNG. The company’s solution is a small-footprint, modularly scalable liquefaction technology based on the HOFIM emission-free compressor, which allows liquefying natural gas locally for storage, transport, and further use in marine, power, and heat generation applications. Through a fleet of cryogenic transport tanks, LNG can be transported over long distances by truck or train to enable the provision of energy to or from isolated regions. LNG links populations or industries with energy sources across distances where pipeline transport is not available or not feasible. Adaptability is part of why natural gas remains one of the world’s top energy resources.

Barrel-type (RB) compressor by MAN Energy Solutions.

One way LNG is being produced is in the process of biogas refining. Brotel expects that the market share for biogas will grow. Utilizing Factory LNG technology at large organic waste collection sites, biomethane – or renewable natural gas (RNG) – can be liquefied from biogas. Biogas or biomethane can be used for combined heat and power (CHP) operations or converted into electricity.

“LNG links populations or industries with energy sources across distances where pipeline transport is not available or not feasible”, said Christian Brotel, MAN Energy Solutions.

When considering the flexibility to connect existing gas consumers with new or remote energy sources, including the growing renewables sector, further LNG development seems logical. However, there are other factors at play. A boom will require the adaption and expansion of gas transportation and storage infrastructure. The focus on electrification and emission reduction of compressor equipment means HOFIM and MOPICO hermetically sealed compressors will see more action, according to Brotel.


Mitsubishi Heavy Industries (MHI) Compressor (MCO) was established in 2010 as a dedicated compressor company under MHI. Takashi Niiyama, Group Manager, Project Development Group, Business Development Division at MCO, highlighted the company’s work in energy transition related markets, such as carbon capture and storage (CCS), carbon capture and utilization (CCU), blue and green ammonia, and hydrogen. The technology used evolved within the conventional fields of ammonia and urea, ethylene/propylene, and propane de-hydro plants. MCO produces large compressor casings with consistent rotor stability. Multi-shaft integrally geared compressors are also available in the MCO portfolio, seeing frequent use in CCS and CCU.

Illustration of a refrigerant compressor driven by a 120 MW dual shaft gas turbine. Courtesy of MCO Compressor.

MCO designs and manufactures LNG mixed refrigerant (MR) compressors according to licensor requirements. For large LNG liquefaction trains, it offers MR compressor packages utilizing the H-100 gas turbine. This grants variable speed operation in a twin shaft design and simplifies plant configuration and start-up, said Niiyama. Full load string tests are done at their Hiroshima facility before shipment to minimize equipment nonconformities. As for mid-scale & small-scale LNG trains, MCO can offer an e-motor drive solution. MCO supplies auxiliary compression services at LNG facilities, such as EFG, booster, and regen applications.

“New requirements are leading to alternative approaches in operation and execution in the LNG compressor market”, said Takashi Niiyama, MCO.

New requirements bring about alternative approaches in operation and execution in the LNG compressor market, said Niiyama. For example, minimizing site work from a construction stand-point and decarbonization trends. Looking ahead, the number of projects adopting modularization philosophies and/or applying e-motor driver in MR compressor strings is increasing.

Modularization, renewable natural gas, and decarbonization are among key trends spurring growth.

LNG Sparks Turbomachinery Growth

, we interviewed several companies to provide a blueprint for the mobile power industry. In this special online feature, we’ll take a closer look Mytilineos, a Greek-based engineering, procurement, and construction (EPC) contractor, operating globally in the energy, metallurgy, power and gas, renewables and storage, and sustainable engineering markets.

Mytilineos works with gas turbine and various technology power plants, including mobile units, which can supply electricity on a fast-track basis. All packages are delivered, assembled, and pre-commissioned so that installation onsite is limited to interconnecting piping and cabling work. Thus, the installations require little to no site preparation and can supply power to the grid in a matter of months or even weeks.

Kostas Horinos, Executive Director of Mobile Power Projects at Mytilineos, explained that the company's mobile plants can run in dual-fuel operation with either natural gas or distillate. Moreover, all the systems related to fuel handling and treatment are also packaged in fully mobile and trailer-mounted form, allowing for quick site delivery. This consistency enables the units to address critical power needs and secure electricity in areas with inadequate generation capacity.

“The mobile power units (MPUs) secure power periods of high demand, such as peak periods during hot months, and extend support in case of damage to existing units,” Horinos said.

Mytilineos uses fully portable MPUs with aeroderivative gas turbine technology that can run up to 35 MW per unit.

“We specialize in creating customized designs for gas mobile MPUs in collaboration with OEMs. Our approach involves utilizing a range of modular accessories to complete the design process quickly and safely, typically within a few months”, said Horinos. This customization extends to the ancillary and auxiliary equipment for the mobile packages, including the main gas turbine trailer, auxiliary turbine trailer, high voltage (HV) substation trailer, electrical auxiliary trailer, and more.

The company can also tailor MPU sets to tackle specific issues.For example, in Takoradi, Ghana, Mytilineos delivered 10 GE TM2500+ mobile gas turbine power packages and full operation and maintenance services, including trailer-mounted balance of plant equipment.

Caption: Mobile power gas turbine packages operating in tandem in Algeria. Credit: Mytilineos.

In Algeria, Mytilineos installed and commissioned 38 mobile gas turbine power generating sets with a total output of 775 MW attained at local ambient conditions. Ninety-seven percent of Algeria’s generating capacity relies on natural gas-fired plants, which equates to about 68 billion kilowatt hours (kWh) per year. With renewables a far way off, the country depends on mobile power to supplement the grid during peak periods.

When evaluating an MPU contractor, several key factors must be considered, Horinos said. First, the contractor's project execution track record should be assessed, along with their project management skills and functional expertise. This is especially important when working with the plug-and-play functionalities of MPUs.

Additionally, the contractor should have the flexibility and capacity to respond to unexpected events and execute multiple projects simultaneously. Another factor is whether the contractor can offer fast-track solutions. Finally, collaboration with full scope operations and management organizations is essential.

Electrification is at the forefront of the energy transition. The key challenge for system operators will be keeping up with electricity demand in real time to avoid blackouts. MPUs can cover this fluctuating demand. This means boosting grid output when consumption rises, or when renewable energy input is insufficient due to intermittent sunlight or wind.

“As a chemical energy carrier that meets the storage and flexibility needs of renewable energy, hydrogen is contained within the decarbonization strategies of many global powers. The EU, U.K., United States, Japan, and China are all exploring ways to progress its use,” said Horinos. “Hydrogen can be used to decarbonize hard-to-abate sectors, such as heavy industry, trucking, aviation, or shipping.”

MPU technology is keeping up with hydrogen advancement. MPUs are not only an effective solution to feed the grid during renewable energy source output fluctuations, but MPU technology also has hydrogen-blend capability to aid in lowering emissions further.

The March/April 2023 cover story provides an in-depth analysis of the mobile power gas turbine market, offering a comprehensive look at the latest trends and developments in this evolving sector.

What Mytilineos does, the impact of its work, and key trends for mobile power

Company Spotlight: Greek Industrial and Energy Company

Modern centrifugal compressors using double-end variable-speed electric motors are high performance, efficient and reliable options for critical compressor services. The compressor train is usually equipped with two compressor casings coupled through two gear units on either side of a double-end variable speed drive (VSD) electric motor. Alternatively, a high-speed VSD electric motor can be used without any gear unit, or just one gear unit for the high-pressure casing.


A compressor of this type can easily compress a large volume of gas from the atmospheric level to a pressure above 150 Barg using a single train with two compressor bodies (casings), and each casing having eight or nine impellers. For some relatively heavy gases, discharge pressure above 250 Barg could easily be achieved using such a compressor train. Modern electric motor-driven compressors offer high reliability and availability, if designed, manufactured, and operated properly. A single shutdown every four years would not be unusual.


Single-end electric motor-coupled to two or three compressor casings have been the traditional configuration for multi-casing centrifugal compressors. One of the problems with a single-end electric motor has been difficulties in accessing the casings in the middle of the compressor train.


An integrally geared compressor is a multi-shaft centrifugal compressor which has different compressor casings, each driven by a pinion gear through a main gear. This is a cost effective and compact compressor option which offers many advantages. Typical benefits are high efficiency, low cost, lightness, and small footprint. Each individual impeller speed can be selected and optimized for the best overall performance and efficiency. The combined compressor package including intercoolers, aftercooler and piping can also be configurated in a very cost effective and compact unit. So which is best?


For process applications which require dry gas seals, a VSD double-casing compressor train might be a better option since the integrally-geared option might require 10 separate dry gas seals compared to four in a double-casing configuration. In addition, variable-speed operation (which could be in the 70%-105% range of nominal speed for double-casing machinery using a double-end VSD electric motor) might offer greater operational flexibility compared to fixed-speed integrally geared compressors. An integrally geared compressor cannot be variable speed due to complexity and design limitations. They use a less flexible inlet guide vane capacity control method.

In high-pressure process gas applications, the VSD double-casing compressor configuration is often a better option than an integrally geared compressor.

It is true that a compressor string with two gearboxes, two compressor casings and a VSD electric motor might result in a complicated torsional situation. In cases where torsional vibration frequencies coincide with resonance frequencies, large torsional deflections, and internal stresses could be generated. Continuous operation under resonance conditions could result in fatigue failure. Overall, however, the dynamic and torsional situation is less complex compared to the ones of integrally geared compressors.
In alternative configurations, high-speed VSD electric-motors with one gear unit or direct-drive arrangement, the dynamic situation is usually more favourable than with gear units or integrally geared compressors. The elimination of one or both gear units can ease the situation. Such a direct-drive configuration can offer better operation, efficiency and reliability.

Another factor to consider is that VSD electric motors generate pulsating torques. Even if the pulsating torques are very small with respect to the main torque, they can excite compressor train resonances with risks of damage to shafts or couplings. But aVSD double-casing compressor can be configured to improve access to bearings, seals and rotating assemblies. This compressor arrangement typically does not require interconnecting piping to be removed for normal maintenance access. Also, the allowable nozzle loads can be two or three times the allowable nozzle loads as per API-617. All these can offer a better piping, access and maintenance compared to integrally geared compressors, which mandate much lower nozzle loads (API-617 ones or even lower). Too often, expansion joints are needed. As an indication, nearly 50% of large integrally geared compressors in critical services have one or more nozzles with expansion joints.


Integrally geared compressors often use many interstage coolers and particularly large numbers of water-cooled heat exchangers combined in a compact package configuration. For a typical integrally geared compressor, the coolers should be supplied by the vendor, and there are more cooled stages and more coolers. In such a compressor package, though, coolers are usually marginally designed (often with minimum margins), and the interstage piping and associated pressure drops can be minimized by locating the intercoolers close to the compressor.


For some facilities, the use of water cooling isn’t an option. Air coolers should be used. In other units, the number of coolers should be minimized. For these cases, double-casings and four cooled sections might be a better option compared to the five or six cooled sections in an integrally geared compressor package.


For some compressor packages, coolers should be designed and fabricated by specialized cooler manufacturers with large margins and special provisions. There is a necessity to exclude coolers from the compressor vendor scope. The coolers should be ordered separately through a specialized cooler manufacturer under the direct supervision of the purchaser. There is a danger that coolers manufactured by independent manufacturers might not be coordinated to be included in a compact compressor package of a typical integrally geared compressor train. For such cases, an integrally geared compressor may not be a good option. The pressure drops between stages for air coolers, or independently provided water-cooled heat exchangers and associated long piping, can diminish the overall efficiency gains from the integrally geared configurations.


Usually, VSD double-casings compressors offer better operation, flexibility, reliability, and arrangement for high-pressure process gas services. They are recommended for many process services rather than integrally geared compressors.


Integrally geared compressors should be limited to specific applications where they can offer definite benefits. The best way to select between these two options is the evaluation of total cost of purchase and operation. Based on experience in nearly 70% of all high-pressure process gas applications, the VSD double-casing compressor configuration is qualified as a better option compared to an integrally geared compressor. On the other hand, there have been applications and services where an integrally geared compressor can be a better option than a VSD double-casing compressor package. There have been cases where the efficiency, compactness, low weight, and lower purchase price of the integrally geared compressor can offer an advantage over other compressor configurations. There have been cases where an integrally geared compressor was the only viable option for a facility. ■

Amin Almasi is a Chartered Professional Engineer in Australia and U.K. (M.Sc. and B.Sc. in mechanical engineering). He is a senior consultant specializing in rotating equipment, condition monitoring and reliability.

Turbo Tips: Comparing Compressors

Siemens Energy and Duke Energy are working together on a hybrid plant in North America to address grid fluctuations. Credit: Siemens Energy.

Siemens Energy and Roland Berger recently released a report highlighting the steps the energy industry needs to take in order to meet decarbonization requirements. The report, titled, 

“Bridging the gap – from perception to reality” 

shows the actions required to meet net zero carbon emissions standards. Torsten Henzelmann, Global Head of Energy and Utilities at Roland Berger, says, “When thinking about collaboration efforts and complex global solutions, we should consider which form of cooperation is the fastest and is best suited for future technologies”. The essence of the report is it will require mutual risk at all levels of industry across the globe to meet these demands.

Specifically, the demands in reference are the “Lower global temperatures by 1.5°C” climate initiative. They’ve concluded that limiting global temperatures to pre-industrial levels is paramount, and many world governments agree, implementing much more stringent preventive policies. Christian Bruch, President, and CEO of Siemens Energy, says, “Each country has different challenges and target positions, so it needs specific answers to drive the energy transition. And this is where the Global Energy Readiness Index comes into play”. That level of specify is key, since not every location can commit equally to the new landscape.

To endure the energy transition, the report lays out five steps. The first is to expand renewables. This includes wind, solar, batteries, hydro, and now nuclear. Secondly, the industry must strive to improve energy efficiency. While many turbomachinery operators are already pushing their equipment into extreme tolerances, more is expected. Third, the electric grid must be strengthened. An easy and effective solution is to invest in more power plants or provide mobile power solutions to key areas without stable access to the grid, such as Texas, California, or Algeria. Fourth, existing infrastructure is to be exploited. Finally, the supply chain must be managed better to optimize costs. It seems to be a very tall order, but one the report claims energy experts look forward to, based on a survey pool of over 2,000 participants.

Each region in the world has a different level of industrial “maturity”, and thus falls at different spots on the energy transition readiness index. For example, North America is 34% ready for the transition, while Europe is 33%. The Middle East and Africa fall behind those at 26%, with Asia Pacific at 25%. Latin America is the least capable of coping with the energy transition, with only 22% readiness on the scale. Certain regions are currently in the process of supplementing fossil fuels to lower carbon emissions, while others are still on the cusp of dropping coal and picking up gas. Even more disparate, some areas have yet to find any reliable power. Care must be taken when applying blanket solutions. This requires investment and research from companies operating in less developed areas of the world to meet these goals, while keeping up with advancing infrastructure and technological needs.

Next on the plate is the case of perceived emissions. Many were asked if they believe levels of CO

 had fallen, remained the same, or increased since 2005. The report also asked what levels would be like in 2030. The report found that a surprising number of participants in the survey believed levels were down since 2005. For Asia Pacific, Middle East and Africa, and Latin America, with their developing economies, emissions have gone up substantially. Estimates bring it as much as 50% for Asia Pacific and the Middle East and Africa. Thus, each part of the world has its own goals for 2030 reduction thresholds. EU and NA want to hit 49% and 46% respectively, while developing regions would be happy to see a 37% reduction.

The report ends by highlighting energy priorities in detail. Top of the list is phasing out coal, which is worse than natural gas for emissions. Next, is the implementation of energy storage solutions. Hydrogen is also mentioned, included in the “Power-to-X” category. Emission markets need to be set up to act as economic incentives to pursue decarbonization. The alignment of these goals across continents, countries, and sectors is the true challenge, one which the report mentions but doesn’t explicitly address. Ultimately, this report should be taken with skepticism and caution. While it sounds good on paper to commit to a greener future, the reality is much of the world is simply not ready to approach the problem. Undeveloped areas of the world need to focus on obtaining reliable electricity, how many greenhouse gases are produced takes a back seat to establishing basic utilities for now.

Analysis of the global energy transition readiness index

What’s Needed to Reach Net Zero

PowerGen International, held Feb. 21-23, returned to Orlando, FL, for 2023. The show appears to be regaining its audience again after a long absence due to the pandemic.

Clarion’s Vice President of Content David Wagman kicked things off by emphasizing the theme of the conference: Destination 2050—reaching net zero carbon emissions by 2050 via industry innovation.

Keynote Jan Aspuru, the COO of Orlando Utilities Commission, discussed its microgrid lab and the development of a hydrogen energy storage system, while Alex Glenn, CEO of Duke Energy Florida and Midwest, detailed different areas that impact the plans to reach net zero, including local and federal government partnerships, maintaining equipment performance, and more.

“Coal will represent less than 5% of power generation in 2030,” he said. “A diverse generation mix is key to customers.”

An early presentation provided an overview of direct air capture (DAC) technology and the status of developments and deployments to date. It included a discussion on potential applications for coupling DAC technology with existing power assets to lower the carbon footprint.

Eric Ping, Vice President, Technology at Global Thermostat, explained his company’s DAC system. Air comes in from the sides and is heated to 200°F. Then the CO2 is extracted at a rate of 400 ppm. It uses amine chemistry in solid form instead of the usual solvent form.

“Direct contact steam stripping delivers latent heat into the system,” said Ping. “Multibed adsorption removes significant plant capital expense.”

He added that front-end engineering design (FEED) studies are ongoing for sites in Texas, Illinois, and Alabama to identify risks, establish a plan of execution, and develop a budget before projects are approved for funding.

Caption: Kevin Siess of DTE Energy showcased a new CHP plant that utilizes digital twin technology to operate the plant with a single person on site. Courtesy of Turbomachinery International.

DTE Energy’s Dearborn Central Energy Plant (CEP) generates electricity and distributes chilled water, hot water, and steam to buildings at the Ford Dearborn Research and Engineering Campus (REC). The CEP consists of a combined heat and power (CHP) plant and a chilled/hot water plant for combined power and steam generation. The energy produced from the CHP is sent to DTE Electric. Steam, hot water, and chilled water are sent to the REC. The CHP plant can generate 34 MW and produce up to 225 kilopounds per hour (KPPH) of 200 PSIG saturated steam. It consists of two 14.5 MW Solar Titan 130 gas turbines, a 5 MW condensing steam turbine from Siemens Energy, and two Rentech Heat Recovery Steam Generators (HRSGs) (370,000 lb/hr).

Kevin Siess, Facility Manager at DTE Energy, said the CEP opened on the first day of 2020. COVID-19-inspired lockdowns provided the impetus to innovate in plant monitoring.

“A single person looks after the entire 34 MW, 87,000-square-foot facility 76% of the time,” said Siess.

Caption: Sessions at PowerGen International 2023 were generally well attended. Courtesy of Turbomachinery International.

Coal-to-gas conversions were covered in several sessions during the show. While some dream of transitioning to renewables in a matter of a few years, reality is beginning to set in. By moving coal resources to natural gas, major emissions reductions can be achieved without causing grid disruption or causing rolling blackouts as has been the case in California of late.

Jonas Hackmann, President of Fossil Power Systems, talked about the many technical and project execution challenges to be considered when planning to convert a tangential fired furnace from coal to natural gas.

Another session noted strong interest in 100% hydrogen firing or co-firing large utility-class coal, oil, and natural gas boilers to achieve decarbonization goals. What surprised some attendees was the fact that running hydrogen in boilers is nothing new.

“We have had a great many package boilers running nothing but hydrogen for decades,” said Denis Osowski, Development Director, Engineering Technology at Babcock & Wilcox.

He questioned, however, whether the use of hydrogen in boilers made sound economic sense most of the time to produce power and steam. In situations where there is a hydrogen hub operating and a coal boiler is sitting nearby, it may make sense. But overall, he said hydrogen is a super-expensive fuel and the use of it may require expensive system and equipment modifications.

Rethinking data center power was the topic of a session toward the end of the program. Todd Forrest

Senior Project Development Engineer at HDR, briefed the crowd that there are already more than 4 GW of data centers in the U.S. in primary and secondary markets, and the market is experiencing 11% year-over-year growth. He doesn’t anticipate that growth rate slowing down any time soon.

The full show report is available in the March/April print issue of 

Dominant themes at the show included hydrogen, the evolution of power plant, and CHP. 

PowerGen 2023 Showcases Innovation 

Historically, the three most frequently reported points for leakage have been: seals; locally damaged or buckled thin shells such as thin-wall casings/piping, large shells, and thin-wall sections; and bolt connections such as flange connections and bolted sections. Many turbomachinery casings, bodies, compo nents, impellers, blades, and rotating parts are thin-wall shells or folded thin plates. Examples are casings, tubular/ cylindrical shell bodies, piping spools, and more. The shells are more complicated than flat plates because their bending cannot, in general, be separated from their stretching. Due to the curvature of the surface, a shell acquires a spatial stiffness that theoretically gives to it a larger load-carrying capacity. Therefore, thin shells have been widely used in many applications. But they are vulnerable to local buckling and damage. Failures in thin-wall shell-like parts and casings have been frequently reported.

Many turbomachinery casings, bodies, components, impellers, blades, and rotating parts are thin-wall shells or folded thin plates. Examples are casings, tubular/cylindrical shell bodies, piping spools, and more. The shells are more complicated than flat plates because their bending cannot, in general, be separated from their stretching. Due to the curvature of the surface, a shell acquires a spatial stiffness that theoretically gives to it a larger load-carrying capacity. Therefore, thin shells have been widely used in many applications. But they are vulnerable to local buckling and damage. Failures in thin-wall shell-like parts and casings have been frequently reported.

The reason that many shells fail at a much smaller load than the classical critical load is due to the combined effect of imperfections, defects, and nonlinearities. In practice, there are random imperfections and defects which affect shells and shell-like bodies. Even in careful experiments, the measured failure loads and collapse modes exhibit tremendous scatter due to random imperfections and defects.

Nonlinearities and imperfections/defects sensitivities manifest in a variety of buckling shapes and different forms of failures. Buckling may show rapid transitions from one shape to another. The buckling of a shell can lead to the leakage, fracture, or even total collapse.

Failures in thin-wall shell-like parts and casings have been frequently reported.

Too often, high imperfection sensitivity and high nonlinearity of mechanical behaviour of shells are the consequence of interactions. There might be many different buckling modes associated with the same or nearly the same buckling load.

Shells are sensitive to transverse forces, especially if they are simultaneously subjected to an axial compressive load. The weakening effect of component imperfections and defects is most pronounced in the range of intermediate slenderness. In those slenderness ratios, critical buckling stress and yield stress are roughly equal. The decrease in strength is most marked for shells and plates of intermediate slenderness subjected to compressive stressing. Unfortunately, these ranges are used in many applications. A pragmatic solution is: 

Verification for shell-like bodies and parts that considers all possible buckling/failures with all realistic details/imperfections/defects.

Alternatively, use sufficient safety factors to cover all buckling/failures to prevent leakage and breakage.


It is desirable to make allowances for abuse which may result from unexpected conditions, operator errors, or the effects of wear and tear on key components, subsystems, members, and connections. Care should be taken for vulnerable points such as thin shells. Stress conditions, manufacturing details, and cracking at or near high stress points in shells are important.

The flexibility offered by bolt connections in the fabrication, installation, operation and maintenance is another factor to consider. Any bolt connection is an expensive joint compared to welding. For bolting connections, many different risks should be mitigated and many requirements should be met. There are always risks of leakage.

Connections (whether welding connections or bolting connections) are important for turbomachines and associated piping. The type and details of connections between major assemblies, subassemblies, and piping spools should be studied with care.

Particular attention is needed for shell-like equipment and thin-wall bodies (large-diameter thin-wall casing, and piping) as they can easily be affected by local yielding and local buckling and subsequently failures. 

Leakage sources include seals, thin shells, and bolt connections

Avoiding Leakage & Breakage

Improvements in wet fogging—a process the directs a fine mist into the inlet airflow of a turbine to cool the air with the goal of increasing power and efficiency—was one of several technologies explored at the Western Turbine Users Inc. (WTUI) conference and exhibition, held in San Diego, California, March 12–15, 2023.

Increasing Turbine Plant Performance by 10% Through Wet Fogging

, ProEnergy Services analyzed various turbine-cooling methods before determining its best investment would be an innovative fogging technology that can be combined with its wet-compression technology for superior outcomes, according to Constantin Dinu, a senior performance engineer at ProEnergy Services. The goal of the system, still under development, is to improve a plant’s power output by 10% percent.

“The project aligns with our efforts to continually improve engine performance,” Dinu said.

Aeroderivative gas turbines, which comprise the company’s client base, have a steeper power lapse than heavy-duty turbines as the ambient temperature increases, which justified ProEnergy’s interest in fogging.

“We operate a couple of plants in Houston, where the weather is hot, and we have customers and projects in areas where fogging makes a lot of sense—that’s one reason we started developing this as an enhancement technology,” he said.

Dinu shared some of the company's findings in its comparison of fogging against other technologies:

Fogging outperformed NOx water over-injection, which had limited impact at high temperatures. NOx water also hurt the heat rate and may impact the combuster and hot gas path life. Based on Dinu’s studies, the maximum benefit shown from increasing NOx water is a boost of approximately 2 MW of power at temperatures typically below 80°F degrees. At higher temperatures, the benefit is limited.

Fogging also outperformed evaporative cooling for a number of reasons, including the cost of the media used in the process. “You can recover an investment in fogging more than twice as fast as for an evaporative system,” he said.

A well-designed and optimized fogging system can achieve an evaporation effectiveness close to 100%. A power generator should select the fogging system with the highest effectiveness, he noted. A fogging system may offer  a 20° temperature drop on a 95° day with about 40% relative humidity, but such numbers are hard to replicate over a plant’s ambient temperature range, Dinu said.

His advice: Familiarize yourself with the evaporative effectiveness and whether that can be guaranteed at your area’s ambient temperature range.

Additionally, the fogging nozzle design is critical as is the water supply pressure, spray characteristics, and distribution of the fogging nozzles.

Articles

After analyzing different turbine-cooling methods, ProEnergy Services decided to innovate its own fogging technology that can be combined with its wet-compression technology.

WTUI 2023 Session Coverage: Fogging Outperforms Other Cooling, Power-Boosting Tech, Fueling an Investment in Innovation

The first in-person Western Turbine Users Inc (WTUI) conference and exhibition of the decade included several companies introducing advances in technology. Industrom Power, a Houston-based startup founded by GE veterans, introduced its ready-to-launch, closed-loop CO

 system that, according to the company, can boost turbine plant power up to 20% at a 17% better heat rate.

“My partner, Joseph Harris, and I saw a need in the industry for something that uses waste heat to generate power and can start as fast as an LM6000. We came up with new technology that can do that,” Industrom CEO Paul Angel said during a presentation at the WTUI conference, held in San Diego, California, March 12–15, 2023.

The self-contained system uses no water and produces no emissions. It is designed to accelerate as fast as an LM6000 gas turbine system and has the capacity to add 10 MW of power, Angel said.

“The system is designed so that you can run the LM6000 any way you want, and we just go along for the ride,” he said.

 and a closed loop is that the internal machinery and heat exchangers can be very small. Industrom installs its system on what it calls a power trailer, Angel said. The turbine, gearbox, generator, and control center sit on a power trailer that is approximately the dimension of a single-wide mobile home and is road legal, “so you can relatively easily bring that into California,” he said. The cooler trailer is about the same size, he said.

Industrom estimates the trailer option saves the installer about $3 million in installation costs. Installation time is about one to two days. The system is available for both lease or purchase.

Angel said Industrom, founded in 2018, is in discussions to launch its technology with a Midwest utility this year.

In this WTUI session, Industrom Power unveiled a closed-loop CO2 system that can boost turbine plant power by up to 20%. The system uses waste heat, does not require water, and produces no emissions.

WTUI 2023: Houston Startup Touts Closed-Loop CO2 System uses Waste Heat to Boost Energy Plant Power 20%

Senet and Heath Consultants are working together to provide natural gas leak detection products, consulting services, and managed LoRaWAN network services to utilities and other natural gas stakeholders in the United States.

To address the demand for safety and efficiency enhancements throughout the gas distribution infrastructure, Heath Consultants and Senet are working with utilities and industry solution providers to support pilots and full-scale deployments of commercially available network-connected AMI residential methane gas alarms for in-building environments.

To learn more, visit with Senet at the LoRaWAN LIVE Orlando conference being hosted by the LoRa Alliance at the Loews Portofino Bay Hotel at Universal Orlando March 15th and 16th.

Digital Natural Gas Leak Detection

The study was led by researchers at the University of Sydney and University of Toronto. Image: Pexels.

A team of researchers at the Universities of Sydney and Toronto have developed a new acid-based electrochemical process for the conversion of captured CO2. The new method uses an acidic reactive chemical. The study rendered a twofold improvement in energy efficiency compared to previous benchmarks.

The catalyst works by applying an acidic electrolyte, with more carbon being utilized for conversion in the process compared with alkaline-based solutions. When being treated with electricity, the CO2 is catalyzed into multicarbon products.

“Until now, converting CO2 into multicarbon products in acidic media has been challenging. Using an adlayer system, the catalyst acquires a reactive environment that is favorable for multicarbon formation at an energy-efficient operating condition,” said Dr Fengwang Li, a corresponding author of the study from the University of Sydney School of Chemical and Biomolecular Engineering.

New process enhances carbon capture and conversion 

Aftermarket Carbon Capture Utilization

The Western Turbine Users Inc. (WTUI) conference is taking place this week in San Diego, California. It traditionally kicks off with a review of the past year’s gas turbine sales and predictions for the coming year. Delivered by Mark Axford of Axford Turbine Consultants and Tony Brough of Dora Partners, the big news is that new gas turbine orders worldwide were up 47% in terms of MW capacity in 2022 compared to 2021.

This increase is particularly welcome after some difficult years. At last year’s show, they reported that new gas turbine orders (in MW) were down 12% in 2021 and that this was part of a longer term downward trend: The annual GT market was sized about 60 GW a decade ago and had dropped into the 30 GW to 40 GW range. It was heartening to see it return to around 50 GW for 2022 and achieve its highest level in more than six years. That number was considerably more than Axford predicted at last year’s WTUI event. He forecast that MW orders would be down overall in 2022.

Unit orders, though, told a different story. They had been up slightly in 2021 compared to the previous year but were slightly down in 2022. Overall, unit orders worldwide have been flat for years, just above 400 per year.

Brough commented that the 2022 surge in MW orders was down mainly to an increase in sales of large gas turbines. He added that orders for these machines tend to be cyclic so not to necessarily expect another jump in orders in 2023 for large-frame machines.

The presentation always ends with a look to the future. Axford expects overall worldwide GT orders to drop in 2023, perhaps down as low as 40 GW. He cautioned, however, that things can change rapidly. Who would have predicted that oil would surge again above $100 a barrel (as it did last summer), that inflation would continue above 6% per year, or that the war in Ukraine would pass the year mark? Such events cause major market disruptions and tend to throw off forecasts. Such unpredictability in the coming months could raise or lower the prospects for GT orders.

Get ready for more WTUI news in the coming days.

Gas Turbine orders skyrocket, up 47% for MW capacity in the last year compared to 2021.

WTUI News: Western Turbine Conference Reports Surge in GT Orders 

Anaergia has commissioned a new biomethane facility in northern Italy, called Ambiente & Risorse, which can anaerobically digest 40,000 metric tons of landfill-diverted food scraps to convert it to 3,900,000 cubic meters of renewable natural gas (biomethane) for injection into the region’s natural gas pipelines. The plant also captures carbon dioxide created in the anaerobic digestion process to create up to 9,000 tons per year of calcium carbonate fertilizer. The new facility is one of six plants Anaergia will have commissioned over two years in Italy, and it helps meet the RepowerEU 2030 biomethane targets and brings Europe closer to its net-zero emissions goals.

Injecting biomethane into region’s natural gas pipelines

EU Bioproduction Increase

Northern Biogas is acquiring three additional dairy renewable natural gas (RNG) projects, significantly expanding its RNG production capacity. Northern Biogas is a waste-to-RNG company, specializing in the development, construction, and operation of domestic RNG facilities. These facilities provide energy derived from organic waste. The acquisition of these three facilities marks growth in the company’s RNG project development pipeline. These RNG facilities are in close proximity to Northern Biogas’ existing footprint and are expected to begin commercial service by the first quarter of 2024.

Renewable Natural Gas Projects

Caption: Chemraz 541 universal black compound applied onto seals. Credit: Greene Tweed.

Greene Tweed is introducing the Chemraz 541, a universal-purpose black compound engineered for reliability in demanding environments such as those found in the Chemical Processing and Oil & Gas industries. Particularly helpful in the presence of acids, amines, aromatics, distilled water, and steam. Chemraz 541 can operate at temperatures of 3°F /-16°C up to 446° F /230°C.

The compound offers better performance due to its tensile strength and modulus. Moreover, its low outgassing values reduce the risk of deposits on sensitive surfaces, while its high elongation values allow easy installation of o-rings. Custom geometry is available upon request.

Chemical resistance for demanding environments and processes 

Chemraz 541 Universal Compound

Assistant Editor, Turbomachinery International Magazine

Fluitron is introducing a commercialized 1 ton-per-day (TPD) hydrogen gas processing system at 520 bar. Because it integrates components for hydrogen inventory management systems, it is ideal for high-flow customers generating hydrogen from MW-size electrolyzers or developing roadside dispensing stations. The system compresses and transfers hydrogen from a low-pressure source to high-pressure gas distribution tube trailers.

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