Hydraulic Power Recovery in Amine Units: Where the Rich-Amine Pressure Goes

A gas-sweetening unit runs its absorber at high pressure and its regenerator at close to atmospheric pressure, which means the rich amine leaving the absorber has to be let down before it can be heated. On 15 September 2026 China National Petroleum Corporation reported that the group's first hydraulic power recovery turbine driving a pump directly had been commissioned in the third phase of the Xushen 9 natural gas processing plant at the Daqing oilfield, and that the technology can bring the unit's overall energy consumption down by more than 30% while saving 4 million cubic metres of fuel gas a year. The same month, the national standard that covers this machine — GB/T 3215-2025 — took effect, replacing its 2019 edition, and its scope names hydraulic power recovery turbines (HPRT) operated by a pump running in reverse.

This article sets out why the pressure in a rich-amine loop is a problem at all, which arrangements exist for recovering it, what the standard record says about the machine, who has put a unit on the record, and where that record stops.

Why is the pressure in a rich-amine loop a problem at all?

Because the loop is built around a pressure difference that has to be destroyed on the way down and re-created on the way up, and both halves of that transaction cost money.

In a solvent-based acid gas removal unit, the absorber is where the solvent meets the gas at pressure: the rising gas contacts descending lean amine, the acid gas is absorbed, and the rich solvent collects in the bottom of the vessel at close to absorber pressure. The regenerator is where the solvent is stripped of the absorbed gas by heat — and it runs at near-atmospheric pressure, because the absorbed gas has to come off as a gas and because the reboiler duty is what pays for the separation. Between the two vessels the rich amine is at high pressure and has to become low pressure. In the simplest arrangement that pressure is thrown away across a level-control valve, and the energy that was put into the amine when it was pumped up to absorber pressure becomes heat in the fluid, which then has to be removed again downstream.

The pump and the valve are two ends of the same calculation. The absorber needs the solvent delivered at its own pressure, so a high-pressure pump — usually a multistage centrifugal machine, and in refinery service very often a barrel pump, a design the standard calls the between-bearings type — supplies the head. The let-down valve dissipates what the pump added. On a unit that runs continuously, that dissipated pressure is a standing operating cost rather than an incident, which is why the loop attracts energy-recovery machines at all.

An HPRT sits on the let-down path instead of the valve. High-pressure rich amine is fed into a machine that is, mechanically, a centrifugal pump run backwards: it takes the pressure as a liquid, extracts the pressure energy as shaft power, and discharges at the reduced pressure the downstream process needs. The shaft power then drives something — and what it drives is the design decision that separates one arrangement from another.

Which arrangements are used to recover it?

Three, and they differ in how tightly the turbine's output is tied to the pump's demand.

The published product record for one Chinese power-recovery turbine line gives the shape of the duty the arrangement has to accept: a flow range up to about 6,580 m³/h, a head up to about 3,250 m, a medium temperature range of 80–420 °C, construction to API 610 (11th edition) in the BB1–BB5 subtypes, blades described as designed for two-phase flow, and the turbine-and-lean-amine-pump integration as an option. Those are catalogue figures for a product family, not results from a named installation.

The machine-class question is the same one an ordinary pump raises, because an HPRT is an ordinary pump run in reverse. A single-stage overhung machine covers the smaller duties; a multistage between-bearings machine covers the larger ones; a barrel or double-casing machine is used where the pressure is high enough that the casing has to be a pressure vessel. What the reverse duty adds is that the machine has to hold a pressure drop rather than build a pressure rise, and that the fluid arriving at its inlet is a liquid that has just come off an absorber — which may carry gas in solution or as entrainment.

What does the standard record say about the machine?

That this machine class sits inside the pump standard rather than in a standard of its own — and that the 2025 edition changed the way the standard states the range it is written for.

The six conditions are the same list in both editions: a discharge pressure of 1,900 kPa gauge, a suction pressure of 500 kPa gauge, a pumped-liquid temperature of 150 °C, a running speed of 3,600 r/min, a rated head of 120 m, and an impeller diameter of 330 mm for an overhung pump. What changed between the editions is the framing. The 2019 edition stated the list as conditions under which using that standard's pumps is beneficial for cost control; the 2025 edition states the same list as the range of liquid the standard's pumps are applicable to. Both editions name the reverse-running energy-recovery turbine in the scope, so the machine has been inside the pump standard for longer than one revision — the 2025 edition restates the boundary rather than introducing the machine.

Two administrative details are worth recording because they decide which edition a specification should cite. The 2025 edition was issued by the State Administration for Market Regulation and the Standardization Administration of China, is administered by the national pump standardisation committee SAC/TC 211, is proposed by the China Machinery Industry Federation, and replaced the 2019 edition in full. Its classification is a product standard, ICS 23.080. The drafting list is long and spans pump works, engineering companies and universities — which is what a standard that has to cover both the pump duty and the recovery-turbine duty looks like.

Who has put a unit on the record?

One operating unit, published as a first for its group, with two plant-level figures attached — and the design institute, not the machine supplier, is the party named.

The unit. China National Petroleum Corporation reported on 15 September 2026 that the group's first hydraulic power recovery turbine driving a pump directly had been commissioned in the third phase of the Xushen 9 natural gas processing plant at the Daqing oilfield. The report states that the technology converts the pressure energy of high-pressure rich amine directly into pumping power, achieving in-place recovery of the energy, and that it can bring the unit's overall energy consumption down by more than 30% while saving 4 million cubic metres of fuel gas a year. The report also states that the application simplified the equipment structure, reduced the number of potential failure points, and improved the reliability and safety of the system. The work is attributed to the design institute of the Daqing oilfield. (Source: the China National Petroleum Corporation website, 2026-09-15.)

The problem the unit is set against. The same report frames the application as a response to two industry problems in the decarbonisation of high-carbon-dioxide natural gas: high energy consumption in the process, and insufficient stability of equipment in operation. Both are statements about the plant, and neither is quantified beyond the two figures above. (Source: the same.)

The product side. One Chinese maker publishes a power-recovery turbine line built to API 610 (11th edition) in the BB1–BB5 subtypes, described as hydraulically designed for the turbine duty rather than for pump duty as such, with a flow range to about 6,580 m³/h, a head to about 3,250 m, a temperature range of 80–420 °C, blades designed for two-phase flow, and the option of integrating the turbine with the lean-amine pump. The listed applications include the hydrotreater feed pump plus turbine train, gas-purification units in coal chemical plants, and the desulphurisation and decarbonisation turbine duties in ammonia plants. (Source: the maker's product page.)

The standard side. The scope change recorded above is itself part of the record: from 1 April 2026 a specification written against GB/T 3215 cites an edition that names the HPRT explicitly, states its six boundary conditions as applicability rather than as a cost-benefit note, and adopts ISO 13709:2009 as modified. (Sources: the national standards public service platform, for the metadata; the standard's published synopsis, for the scope text.)

Where does this route stop?

At five places, all of them visible in the published record.

The energy figure is a plant figure. A reduction of more than 30% in a unit's overall energy consumption and 4 million cubic metres of fuel gas a year are figures about a gas-processing plant. They are not the recovered power at the turbine shaft, not the turbine's efficiency, and not the pump's efficiency. Reading them as a machine performance number would merge a plant-level result with a machine-level claim that has not been published.

There is one unit and no operating window. The report is a commissioning announcement. It does not state the rich-amine flow, the inlet and outlet pressure of the turbine, the pressure differential it works across, the shaft power recovered, the running hours accumulated, or the time between the commissioning and the announcement. There is no service record in the published material, and no independent performance measurement.

The pressure at which the loop runs is not published. The account states that the recovered energy is the pressure energy of high-pressure rich amine, but gives no pressure. What can be said from the process description is only that the absorber runs at pressure and the regenerator does not; the actual differential that the machine works across is not in the record, and it is the differential that decides how much power is available.

The two-phase capability is a product statement, not a test result. That the medium arriving at the turbine inlet may carry gas, and that a maker's blades are designed for two-phase flow, are product-positioning statements. No entrained-gas fraction, no two-phase test condition and no degradation figure appears in the record for the commissioned unit.

The standard is a specification, not a performance record. GB/T 3215-2025 states requirements, classifications, design rules and the boundary conditions under which it applies. It contains no recovered-power figure, no efficiency figure and no service-life figure. Its relevance to a project is the set of rules a machine has to be built and tested against, and the edition that applies changed on 1 April 2026.

Put plainly: the published material answers where the pressure energy can go. It does not answer how much of it arrives, and it does not answer which machine should be selected for a given duty.

What does the trend add up to?

Three movements are visible, and they sit at different levels of maturity.

The machine moved from a separate energy-recovery device towards a driver. The direct-drive arrangement in the published unit takes the turbine's output straight into the pump and removes the motor from that shaft; the clutch and integrated arrangements keep the motor but reduce its load. All three end in the same place: the pressure that the loop used to dissipate becomes part of the train's power balance rather than a heat load to be removed.

The standard moved the machine into the pump family and restated the boundary. Both editions of GB/T 3215 since 2019 name the reverse-running recovery turbine in the scope; the 2025 edition states the six duty conditions as the range the standard's pumps are applicable to, and adopts ISO 13709:2009 as a modified adoption. For anyone writing a specification, the practical effect is that the edition cited now matters: the 2019 edition was withdrawn on 1 April 2026.

The economic argument moved from machine efficiency to loop design. The published case is not a claim about a better turbine; it is a case about a plant that removed a standing energy loss from a loop that runs continuously. That is a system-level argument, and it is consistent with the standard's own framing, which treats the six duty conditions as the conditions under which this pump family is the applicable choice.

What has not moved is the evidence type. Every figure in this article is a standard requirement, a catalogue value or an operator's own statement about a plant, and the only operating unit on the record has one commissioning announcement behind it.

What this article does not cover

Note that this article does not select a pump or a turbine, size a machine, calculate head, net positive suction head or recovered power, specify a material, a seal or a coupling, or give prices and delivery times. It describes the duty, the standard record, the arrangement options and the boundary of that evidence. It is not a purchase specification and it carries no compliance determination.

Where the next constraint sits

The constraint that follows this one is not hydraulic but regulatory, and it lands on the same loop. The seals and gaskets in an amine service are chosen for chemical resistance across a wide medium list — and the fluorinated materials that usually provide it are the subject of a restriction process in the European Union that has produced opinions but no adopted text. PFAS and Pump Seals: What the Restriction Timeline Changes in Wetted-Material Choice sets out where that process stands and which parts of a pump it reaches.

The other adjacent duty changes the direction the pressure is doing work in. CO₂ Injection Pumps: Why the Clearance Volume Decides the Efficiency takes a fluid whose density moves steeply with pressure and temperature, and shows why the volume left in the valve chamber — not the pressure alone — sets the efficiency of a machine that has to raise pressure rather than recover it.

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