Aug-2022

Power-to-X integration, the methanol case

Renewable power to methanol projects can provide an economically attractive route to renewable methanol production.

Raimon Marin
Afry

Article Summary

Power-to-X (PtX) technologies use electricity, preferentially renewable electricity, to produce hydrogen via electrolysis of water, with oxygen and low-grade heat as the main by-products. The hydrogen is further used in a range of applications, shown in Figure 1; namely, e-methanol, e-ammonia, synthetic natural gas, synthetic sustainable aviation fuel, direct reduction of iron, and many more.

Integrating small and medium PtX projects into existing facilities is an attractive approach already taken by several players in the industry (S&P Global, 2020) due to the revalorisation of side streams and potential reduction of the CO2 footprint of the existing facility. For PtX applications like methanol and other synthetic hydrocarbons, pulp mills or bio-waste to power are a good fit since there is availability of biogenic CO2 and possibly a reliable supply of renewable electricity. Here, a seamless integration is required for financial success, and it must be made by players with expertise along the whole project value chain (from market analysis and levelised cost of electricity/hydrogen and final product to understanding the technical particularities of pulp mill/bio-waste to power, carbon capture, and PtX). AFRY(c)has a long tradition in market analysis and both pulp mills and bio-waste to power plants with know-how in carbon capture and PtX, as shown in Figure 2, with a track record of successful PtX integration projects.

Selecting the hydrogen plant
Hydrogen is the pivotal element in PtX; selecting the right technology that better adapts to your process needs will help you succeed in your project. Currently, two main technologies can be readily deployed at a certain scale, say more than 20 MW. These are alkaline electrolyte (AEL) and polymer electrolyte membrane (PEM). There are also other technologies in the pipeline at different stages of maturity (such as solid oxide electrolyte and anion exchange membrane); however, none have yet been deployed and operated at any significant industrial scale.

Common knowledge says that PEM is well suited for fluctuating power inputs (like those in wind and photo-voltaic farms), whereas AEL has better efficiency at the cost of lower flexibility in rapid turn-down/up scenarios. Although true, that is a rather simplistic approach, and it could lead to costly pitfalls when designing hydrogen plants above 100s MW. Through experience, we have developed the know-how in managing and executing the design and optimisation of medium- and large-scale electrolysers of either technology in a way that works better in terms of plant availability and flexibility, project finance, power profile, and any other constraints you may encounter. Furthermore, we can forecast both electricity and hydrogen price, which is key to optimise hydrogen plant size and the storage facility (should this be needed).

The X in the equation
The value chain in PtX is very wide and aims at servicing many industries, as seen in Figure 1. Applications that may be easiest to adapt are those that traditionally use hydrogen, such as fuels, ammonia, methanol, and direct reduction of iron. All these processes and applications have well-established and reputable equipment vendors and process licensors. Our role at AFRY is to work as the ‘glue’, integrating every part of the project value chain, from licensed processes, electrolyser equipment and balance of plant, compression and storage, utilities from existing facilities (should it be a brownfield project), and developers’ and owners’ interests.

e-Methanol
Methanol has a vital role in our daily life, being fundamental to the commodities value chain and one of the most promising sustainable fuels for the shipping industry (Maersk, 2021). The main feedstocks to make e-methanol are hydrogen (or electrical power and water) and CO2. Other inputs to the process are low/medium-pressure steam for carbon capture and methanol distillation, compression power, and other utilities.

As discussed above, to extract maximum value from e-methanol, the CO2 must come from biogenic sources, which are abundant in pulp mills and bio-waste to power plants. There are various ways of integrating the PtX plant into the CO2 provider facility. An example would be to route the steam demand from the carbon capture and methanol plant into the pulp mill or a bio-waste to power plant, aiming to minimise its cost and loss in power production. Another example of process integration would be dealing with side streams; for example, oxygen is freely produced in PtX as a by-product. Although oxygen has a well-established market, it is quite often a saturated market; hence, finding new off-takers may be challenging, especially if the market becomes flooded with oxygen from many MW (or GW) scale PtX projects. One option is to find a nearby off-taker, like the pulp mill itself. Here, knowing intimately how a pulp mill operates creates a leading advantage for the project by monetising this side-stream that otherwise would have been vented or sold at a marginal price. This is another example of how partnering with an engineering specialist in PtX and associated industries can give you the extra edge in your project’s viability.

Case study: viability of integrating an e-methanol facility in a pulp mill
A pulp mill was considering revalorising ca. 70 MW of surplus electricity by producing e-methanol. The three main operating units to deploy are: the hydrogen plant (electrolysis-based), carbon capture and conditioning, and the methanol synthesis loop. Figure 3 shows a representative diagram of the main units in an e-methanol facility.

Biogenic CO2 is abundant in pulp mills and, as such, was not a limiting factor in sizing the e-methanol facility. Amine-based carbon capture technology for flue gas applications was selected in this project as a proven way of recovering CO2. The content of CO2 in the flue gas was around 15 vol%, whereas the purity of CO2 recovered was more than 98 vol%, with the balance being mainly water. The front end of the carbon capture plant was designed to remove particulate matter, SOx, and NOx, although it was important to ensure there was no sulphur slip (from reduced species) in the recovered CO2, which would irreversibly damage the catalyst if it slipped through to the methanol synthesis loop. The technology to remove reduced sulphur species is readily available; however, proper sulphur speciation is required for an adequate design. The flue gas from the recovery boiler comprises <10 ppmv of reduced sulphur, of which >80% is Hâ‚‚S and the balance light sulphur organic species. The low-pressure steam needed to run the reboiler in the carbon capture section is taken from the main facility condensing turbine.

Hydrogen production was the limiting factor in this case study (in fact, renewable power to produce hydrogen) and very likely in most projects of this type. Given the power profile available, alkaline water electrolysis was well suited. The hydrogen generated is at 99.95 vol% purity, the balance being mostly moisture since the deOxo catalytic unit depletes oxygen that slips with hydrogen. The oxygen by-product is sent back to the mill as a chemical consumable, creating a credit for the e-methanol facility.