Decarbonising Manufacturing. Paper 2: Options for displacing natural gas, and how to do it economically.

Before looking at options to replace gas, here is the way NOT to decarbonise process heating:

?1.???? Collect the name plate rating of your existing heating system and delivery temperature.

2.???? Find an alternative piece of equipment to delivery this identical duty.

It does NOT make sense to try to replace like with like when changing process heating away from fossil fuels.

?Businesses should instead approach the decarbonisation task as an opportunity to achieve a step change improvement in energy efficiency and productivity. And this means looking at process heating needs in detail, and looking for ways to eliminate central boilers and steam distribution systems by locating new heat sources close to the location where the heat is used, and aligning the delivery temperature with the end requirement.

?Here is what is why we would like to eliminate fossil central boiler and steam systems:

?1.???? The steam is generated centrally and distributed through steam piping, and then condensate must be collected and returned to the boiler. The losses in these distribution systems can be up to half of the steam generated in extreme cases, and these systems are always a major ongoing maintenance task to keep losses manageable. So why perpetuate them?

2.???? The heat is generated at the highest temperature needed in the whole factory Plus a large allowance for heat losses and heat transfer requirements. Individual plant processes often don’t require such high temperatures and may not need steam at all, and you can see that even without considering process redesign and heat recovery to reduce heat loads further. This becomes critical when heat pumps are considered to supply process heat, as the efficiency of heat pumps decreases as the temperature between the waste heat and process temperatures increase, and there is a much smaller choice of heat pumps to supply temperatures above 90C, and their price is significantly higher.

3.???? These systems are large, complex, having manning requirements, are hot and have significant safety issues.

?Options for replacing natural gas for heating: There are multiple potential paths to decarbonise process heating in a facility and often a hybrid system is best:

?·?????? Electrification, with zero carbon electricity supply.

o?? Heat pumps – this is well established technology for supplying hot water up to 95C in heating and drying applications and are becoming commercialised for temperatures up to 250C steam. They offer great efficiency improvements, having COPs of 3-5+ for heating, and by using the cold side of the heat pump for cooling simultaneously, can be much higher again overall (e.g. in drying applications recovering latent heat). This means a multiple of heat output per unit of electricity supplied, and this can more than overcome the relatively high cost of electricity vs gas on a straight $/GJ basis. There are lots of good applications of heat pumps which offer 4-8 year paybacks at current gas/electricity prices, but the returns can be better if the heat pump is designed into the process, you can use the cooling as well as the heating, and you are able to eliminate all steam distribution with attendant losses. Whether this return meets businesses hurdle rates may depend on the premium placed by the business on investments for carbon mitigation. Note that the renewable electricity may come from PV generation on site, but in future it may become more challenging to supplement this by purchasing renewable energy certificates as there is increasing pressure time stamp certificates to ensure purchased renewable energy aligns with the time it is being applied, to avoid greenwashing claims.

o?? Electrode boilers – well established for the full range of steam temperatures supplied by natural gas, but running costs are very high as the efficiency is max 95% and the cost of electricity is 3-5X the cost of gas. They are useful for small localised high temperature steam applications where heat pumps are replacing all the lower temperature bulk heating applications.

o?? Direct electric heating is developing increasing applications in non-metallic mineral processing, and electric arc heating is used for steel making from scrap.

·?????? Biogas to displace natural gas (in existing or new boilers). There is significant opportunity for increasing the generation and use of biogas from anaerobic digestion of wastes, including co-digestion of multiple forms of waste in centralised facilities. To be economical, the waste should be available near the facility, and this is more likely to be the case in rural locations. It is not economical to pipe biogas to a remote location. A key challenge with new AD applications is the shortage of expertise available to design plant for a/multiple particular feedstock(s), and to optimise operation and to keep plants operating at consistent output.

·?????? New biomass boiler. There is also opportunity for increasing use of biomass, providing the site can secure a consistent volume and quality of the waste material, and you can cost justify the relatively expensive solid fuel boiler, the space requirement including storage and materials handling, and the logistics and social license issues for getting material in an out of the site and waste combustion emissions. As a result, this option is also largely constrained to rural applications.

·?????? Solar thermal. Economical applications are limited as the plants are material and space intensive and still require a standby heating or storage system, and the resulting low utilisation of the solar plant generally makes costs uncompetitive with other options.

·?????? Hydrogen. There is no economical application to burn green hydrogen. This is a non-starter.

What is the process to decarbonise a site?

·?????? Develop a roadmap for decarbonisation with clear targets and parameters in line with the company’s long term policy. Having this long term and regularly updated plan is important to align decarbonisation activities with broader capital investment plans.

·?????? Energy and Mass Balances. As mentioned, it is not simple to electrify a site energy efficiently and economically. It requires detailed understanding of processes, and mass and heat flows across a site. Many sites don’t have adequate instrumentation to access this information readily. In complex continuous processes, it may be necessary to do a process integration (or pinch study). When implementing heat pumps to recover heat from refrigeration systems it is necessary to understand how to do this integrated with the operation of the refrigeration plant. As Jarrod Leak offered ‘many designers don’t know how to optimise the equipment design and electricity supply.? I reckon only 30-40 people in the country really know what they are doing for C&I.? And then there is the challenge of electricity supply optimisation where no discipline has the full picture – chemical/mechanical engineers focus on the plant, electrical engineers focus on the supply, and no one discipline is responsible to optimising overall with on-site PV, thermal storage, battery storage, demand response, FCAS etc. See Paper 3. for more insights on this topic.

·?????? Government support: Most manufacturers need significant hand holding through the design phase through to the business case and then onto the implementation of the solution. And many projects need some level of financial incentive through grant funding to overcome perceived risk and make the decarbonisation projects work commercially to surpass normal investment hurdle rates. Most manufacturers cannot take on significant additional debt, particularly to fund long payback (and higher risk) projects. Derisking is essential if we want rapid progress – See Paper 3.

Keep your eye out for the next papers in this series:

?3. The critical need for designing in load flexibility, and the role of the electricity industry

4. Barriers to rapid scale-up and recommended government interventions to move things along at the pace required

5. Potential business models and financing to support change

6. Research needs to support this change

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