HiiROC ($34M to develop thermal plasma electrolysis of natural gas for producing clean hydrogen)

HiiROC, a UK cleantech startup founded in 2019, develops Thermal Plasma Electrolysis technology that converts natural gas to clean hydrogen with no CO₂ emissions. This technology is economical, as it is as cheap as Steam Methane Reforming (SMR) without needing Carbon Capture, Utilization, and Storage (CCUS).

Challenges: hydrogen fuel

The majority of the world’s hydrogen (over 60 million tons) is currently produced via steam methane reforming (SMR) process, which requires a significant amount of energy input and emits a substantial amount of CO₂. The SMR process emits between 5 and 9 tons of CO₂ per ton of hydrogen (H₂) produced.

HiiROC Technology

HiiROC has developed methane pyrolysis technology that synergistically combines the plasma torch and liquid metal reactor to efficiently convert methane into hydrogen and carbon. This technique produces hydrogen at the same low cost as SMR while emitting no CO₂.

HiiROC hydrogen

The schematic diagram below depicts the methane pyrolysis reactor. The reactor consists of a plasma torch and liquid metal circulating system. The liquid metal circulating system contains metal (such as lead or bismuth) that is liquid at operating temperature but solidifies when the plasma torch is turned off.

HiiROC's methane pyrolysis reactor — HiiROC’s methane pyrolysis reactor (ref. WO2022219342A1).

During operation, preheated methane feedstock (about 72 kg/h) is injected into the plasma torch. Through the action of the plasma torch spark, methane instantly decomposes into hydrogen gas and carbon at 6,000 ºC and 50 bar. These high temperature products are directed into a liquid metal racetrack, from which liquid metal and the plasma torch’s products are fed into the main liquid metal reactor that contains a swirl chamber. Additional methane is introduced into the liquid metal swirl chamber for thermal pyrolysis.

The liquid metal in the swirl chamber circulates and initiates pyrolysis of the input methane at elevated temperature and pressure (800 to 1,000 ºC and 50 bar). The circulating liquid metal also functions as a centrifugal separator, separating carbon particles towards the center of the rotating column.

Carbon is then extracted from the reactor’s base via a carbon output. Hydrogen is released from the top of the reactor as it rises from the liquid metal. The hydrogen output product has a high temperature and is used by a heat exchanger that regulates the temperature of feedstock methane.

HiiROC has resolved the carbon buildup problem in the plasma torch. Carbon buildup can clog the torch, significantly reduce process efficiency, and result in significant maintenance downtime. HiiROC discovered two methods to prevent such carbon buildup.

(1) HiiROC has used a porous anode in the torch so that hydrogen output through the anode provides a protective curtain along the inner wall of the anode, preventing carbon buildup.

(2) HiiROC has designed the passage of gas through the plasma torch’s structure. The gas inputs in the electrode protective ceramic deliver methane tangentially into the chamber, thereby creating a helical path in the output gas adjacent to the chamber wall and a vortex within the plasma torch chamber. This configuration not only provides the hydrogen product with significant velocity towards the plasma torch’s output, but it also prevents carbon deposition on the wall.

HiiROC’s innovative combination of the plasma reactor and liquid metal reactor not only achieves an efficient methane pyrolysis, but also improves the torch’s operation and extends its service life.

Once the plasma torch is stopped, liquid metal enters the torch chamber. As shown in the diagram below, a portion of the plasma torch’s electrodes is submerged in liquid metal, which solidifies as the torch cools. The solid metal forms a conductive plug and protects the electrode from aging.

The formation of a solid metal plug in the plasma torch after it stops.

Typically, a plasma torch is restarted with a high voltage pulse, which has a significant aging effect on the electrodes and the torch structure. If liquid metal has entered the torch chamber and solidified to form a plug, the effect of starting the torch is significantly softened. Such a conductive solid metal plug connects the plasma torch’s electrodes, so the high voltage pulse induces a high current (perhaps 200 A) through the plug, causing the metal to rapidly heat and melt.

Upon melting of the conductive plug, the liquid metal enters the liquid circulating system. This is accomplished by using a gas pressure provided in the plasma torch behind the conductive plug, or by using a vacuum provided between the conductive plug and the liquid circulating system.

HiiROC Patent

WO2022219342A1 Method for operation of a plasma torch in a chemical reactor
WO2022219338A1 Plasma torch and method of operation
WO2022219340A1 Gas supply to plasma torch

HiiROC Technology Applications

Clean hydrogen

One of the key applications of HiiROC’s technology is the production of hydrogen. The hydrogen produced can be used as a clean fuel in various sectors, including mobility, gas grid applications, and as a zero-carbon energy carrier. HiiROC’s technology is being used in a manufacturing plant in Germany, which is set to produce 400 kg of hydrogen per day.

Carbon black

Another application of HiiROC’s technology is the production of carbon black from biomethane, flare gas, or natural gas. The carbon black byproduct can be used in tyres, rubbers, plastics, inks, and toners.

HiiROC Products

HiiROC plans to construct a facility in Germany with Wintershall Dea and VNG that will have a nominal capacity of 400 kg of hydrogen per day, equivalent to nearly 5 GWh of annual energy output.