The purchase price of a desulphurisation system is easy to compare. What it costs to operate for the next ten or fifteen years is much harder to know.
Two systems may perform the same basic task of removing hydrogen sulphide from biogas, but require very different levels of chemicals, consumables, maintenance and operator attention once they are running.
That is why CAPEX only tells part of the story. For plant owners comparing desulphurisation technologies, operating expenditure can have a major influence on the economics over the lifetime of the system.
What drives the cost of H2S removal?
The answer depends partly on the chosen technology. Some costs are continuous, while others appear periodically through maintenance, cleaning or replacement.
Typical cost drivers include:
- Chemicals and consumables: including continuous chemical dosing, replacement media, water or nutrients, depending on the process.
- Operator time: the monitoring, adjustment and manual intervention required to keep the process stable.
- Maintenance and cleaning: including service work and the replacement or cleaning of process components.
- Downtime: periods where cleaning or maintenance reduces system availability and potentially affects production.
- Equipment lifetime: how long components and process media can remain in service before replacement is required.
- Impact on downstream equipment: because gas treatment also affects the processes and equipment receiving the cleaned biogas.
No single item necessarily determines the economics. The important point is that these costs continue after commissioning.
Over a long operating life, recurring expenditure can significantly change the comparison between two systems that initially appeared similar; or make a lower purchase price less decisive than it first seemed.
Biological desulphurisation changes the operating model
Biological desulphurisation removes H₂S using naturally occurring sulphur-oxidising bacteria.
In our bio trickling reactor, biogas and a controlled amount of air enter the reactor while recirculated liquid flows through structured packing material. The packing provides the moisture and conditions required for the bacteria, which oxidise the hydrogen sulphide as the gas passes through the reactor.
The process liquid is recirculated, with water and nutrients added periodically to maintain stable operation. Unlike a process based on chemical treatment, it does not depend on continuous chemical dosing during normal operation.
This creates a different operating cost profile:
- no continuous chemical dosing during normal operation
- recirculation of the process liquid
- periodic water and nutrient dosing
- relatively stable input costs, compared to chemical H2S removal
- PLC-controlled operation that reduces manual operator intervention
- packing material designed for cleaning rather than routine replacement
- system availability above 98%
The point is not that every operating cost disappears. Biological processes still require water, nutrients, monitoring and maintenance. The difference lies in what the system consumes, the volatility of the price of the consumable, how much operator intervention it requires and how maintenance is carried out.
In our DS-BTR systems, operating costs are typically 80–90% lower than with conventional chemical gas purification systems, although the actual economics depend on the individual plant and operating conditions.
Cleaning also has an operating cost
Maintenance costs are not limited to spare parts or labour. The time required to carry out the work can matter just as much.
Sulphur and gypsum accumulate in a biological reactor and need to be removed. If cleaning requires packing material to be taken out, the procedure can become both labour-intensive and time-consuming.
Our Quick Sludge Removal system takes a different approach. The reactor is filled with water and pressurised air is introduced from below, cleaning sulphur and gypsum from the packing while it remains inside the reactor.
The packing is designed for repeated cleaning, so with QSR there is no need to remove and replace it as part of the cleaning process. This reduces the time required for cleaning and helps limit downtime.
That distinction matters in a TCO calculation. A maintenance procedure has both a direct cost and, potentially, a production consequence.
Cost does not stop at the desulphurisation system
Desulphurisation rarely operates in isolation.
Cleaned biogas may feed a gas engine or CHP system, a biomethane upgrading plant, fuel production or a liquefaction process.
This means availability and gas quality should be considered in the context of the wider plant. If gas treatment is interrupted or does not perform as required, the effect may extend to the equipment and processes that depend on the cleaned gas.
A useful TCO comparison therefore looks beyond the gas-cleaning unit itself. It considers how reliably the system supports the process around it and what operating consequences follow when it requires attention.
Looking beyond the purchase price
CAPEX remains an important part of any investment decision. But on its own, it cannot show how much a desulphurisation system will consume, how much operator attention it will require or how maintenance will affect plant availability.
A lower purchase price can still be the right choice. But without the operating costs, it is not the full comparison.
