Can high-pressure hydrogen be used as a working medium for expanders?

Ah, using hydrogen as the working medium for an expander? Playing with fire!

Expander: A machine that utilizes the principle of reducing gas temperature by converting the mechanical work generated during the expansion of compressed gas into pressure drop, thereby producing cooling effect. Expanders are commonly used in cryogenic equipment. Expanders are classified into piston expanders and turbine expanders based on their mode of operation and structure. Piston expanders are mainly suitable for small and medium-sized high and medium-pressure cryogenic equipment with high pressure ratios and low flow rates. Compared with piston expanders, turbine expanders feature high flow rates, simple structure, small size, high efficiency, and long operating cycles, making them suitable for large and medium-sized cryogenic equipment. 　　A piston expander is an expander that causes gas to expand in a variable volume to produce external work for cooling (usually, an electric motor is used to absorb this external work). This type of expander is available in both discrete and horizontal types. The vertical structure is more commonly used; components such as the crankshaft, connecting rods, crosshead, piston, intake valve, and exhaust valve are the moving parts, which are installed in the engine housing, cylinders, and intermediate bearings. Its function is similar to that of a reciprocating piston compressor, but its intake and exhaust valves are opened and closed at specific times by intake and exhaust cams. Due to losses of cooling capacity caused by flow resistance of the intake and exhaust valves, incomplete expansion, frictional heat, and heat exchange between external and internal sources, the adiabatic efficiency of piston expanders is generally 65–85% for high-pressure expanders, and 60–70% for medium-pressure expanders. Valveless and single-valve expanders, which emerged in the 1950s and do not rely on cam mechanisms, reduced the number of moving parts in the expanders and improved their operational reliability; they have been widely used in small cryogenic devices. In the 1960s, polytetrafluoroethylene sealing elements with fillers were used to replace oil-lubricated metal sealing elements, preventing lubricating oil from entering the deep cryogenic distillation or liquefaction areas and thus ensuring safety. 　　A turbine expander is an expander that transfers energy through the change in velocity of a gas as it expands. These expanders come in single-stage and double-stage versions, as well as vertical and horizontal types; they can also be of the impulse type or the reaction type. A single-stage centrifugal radial-flow reaction type is generally used, with the external work generated being absorbed by a generator, blower, or oil brake. It is similar to a single-stage centrifugal compressor, but it has vanes (adjustable blades) for regulating the air intake volume. Low-speed bearings are lubricated by forced oil, while high-speed ones use gas bearings. Due to nozzle losses, impeller losses, residual velocity losses, disk friction losses, leakage losses, cross-flow losses, and external heat intrusion losses, the adiabatic efficiency of turbine expanders is generally: 65–75% for medium-pressure expanders, and 75–85% for low-pressure expanders. In the 1960s, liquid-expanding machines were developed, which were mostly used in natural gas separation equipment.

4NM3/H – that’s an extremely small amount; it’s not worth it. The energy saved by the previous expansion machine was very limited, and it would take countless years to recoup the costs! Additionally, hydrogen is too dangerous. As far as I remember, methane is acceptable; for example, in ethylene separation processes, if there is a large amount of methane at the top of the demethanization tower, an expander can be considered, as this offers higher efficiency compared to direct throttling expansion

Reply to 1# Comrade Li: 1. The traffic volume is too low; it’s likely that the energy recovered isn’t sufficient to cover the cost of the equipment investment 2. It’s a bit too dangerous, anyway I’ve never heard of hydrogen expansion engines

There are two major challenges in the design of hydrogen expanders: 1. Sealing and explosion prevention – oil turbines are not suitable for this purpose; 2. It is difficult to calculate the thermodynamic parameters, as there is a large discrepancy between theory and practice. If gas bearings are used, there are currently no mature domestically produced hydrogen-lubricated bearings available

Our facility currently operates at a pressure of 5 MPa and handles 200,000 NM3/h of hydrogen; we want to increase this pressure to 25 MPa. Could you please advise on how this capacity can be utilized again?

Are there any manufacturers that produce hydrogen expanders currently? What are the main technical challenges and risks?

The pressure parameter is incorrect, right? It can’t get smaller as it expands.