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Coke plants recover ammonia every day during coal gas purification. Yet many of them continue to purchase limestone for flue gas desulfurization. The ammonia is produced on site, but it is not being used where it could create greater value.
This is an overlooked cost in coke plant operations.
During coal carbonization, raw coke oven gas contains not only tar and crude benzene, but also ammonia. The ammonia is recovered through the ammonia-stripping process and converted into ammonia water or concentrated ammonia gas. In a normally operating coke plant, the recovered ammonia can provide a substantial part of the absorbent required by a flue gas desulfurization (FGD) system.
At the same time, the plant's desulfurization system may still rely on externally purchased limestone. These two processes have operated independently for years. But as gypsum disposal costs, carbon costs and ammonia slip requirements become increasingly important, this traditional arrangement deserves a closer look.
Three Costs Hidden in the Existing Desulfurization Model
1. The cost of gypsum disposal
Limestone-gypsum desulfurization converts absorbed sulfur dioxide into gypsum. This by-product must be properly handled and disposed of in accordance with environmental requirements.
In 2026, reported disposal prices for desulfurization gypsum in different regions generally ranged from RMB 70 to RMB 176 per tonne. Although coke plants may produce less gypsum than large power stations, the material is generated continuously, making disposal an ongoing operating expense.
2. The cost of carbon emissions
Calcium-based desulfurization releases approximately 0.75 tonnes of carbon dioxide for every tonne of sulfur dioxide absorbed. With carbon prices exceeding RMB 95 per tonne during the second half of 2026, carbon emissions have become a more direct operating cost rather than a distant concern.
3. The opportunity cost of underutilized ammonia
Ammonia recovered within a coke plant may be sold at a relatively low price or consumed as an alkali source in the HPF desulfurization process. Meanwhile, the flue gas treatment system continues to purchase limestone and pay for gypsum disposal.
In other words, the plant already has an available alkaline resource, but it is not being used in the process where it could potentially deliver greater economic value.
Together, these three costs point to a structural issue: coke plants are not necessarily short of resources. The problem is that their existing resources are not being used as part of an integrated process.
Bringing Recovered Ammonia Back into Flue Gas Desulfurization
Ammonia-based flue gas desulfurization offers a way to connect ammonia recovery with flue gas treatment.
Ammonia water recovered from the ammonia-stripping section typically has a concentration of around 5%–10% and can be used as the absorbent in an ammonia FGD system.
During desulfurization, ammonia reacts with sulfur dioxide to form ammonium sulfite. The solution then undergoes oxidation, concentration and crystallization to produce ammonium sulfate fertilizer.
There is also an opportunity to make further use of the ammonia. Unreacted ammonia can be recovered through evaporation and used as a reducing agent in a selective catalytic reduction (SCR) denitrification system. This creates the potential to integrate the ammonia supply for desulfurization and denitrification.
The process connects several stages that would otherwise operate separately:
Ammonia recovery from coke oven gas purification
Sulfur dioxide removal through ammonia-based FGD
Ammonia recovery and utilization
Ammonium sulfate production
Ammonia supply for SCR denitrification
Instead of purchasing limestone and generating gypsum that requires disposal, a coke plant can use recovered ammonia to remove sulfur dioxide and produce ammonium sulfate as a marketable by-product.
The value of ammonia desulfurization therefore lies not simply in changing the absorbent. It lies in making better use of resources already available within the plant.
Ammonium Sulfate Provides a Market Outlet
For coke plants considering ammonia desulfurization, the destination of the ammonium sulfate produced is an important part of the investment decision.
In July 2026, new export inspection requirements for ammonium sulfate came into effect, triggering significant price fluctuations. In Shanxi, coke-grade ammonium sulfate prices reportedly fell to RMB 600–640 per tonne. By September, after the transition period ended and export procedures became more standardized, mainstream prices had recovered to approximately RMB 963–1,015 per tonne.
These fluctuations reflect changes in product quality requirements and compliance costs, rather than the disappearance of market demand.
Ammonium sulfate serves an agricultural market supported by demand for both nitrogen and sulfur. In areas where sulfur-deficient soils and sulfur-demanding crops are common, its dual-nutrient properties provide a clear application.
The quality of coke-grade ammonium sulfate can vary, so product quality and compliance with agricultural fertilizer standards remain important. However, ammonium sulfate that meets the relevant standards has established market channels.
This gives ammonia FGD a different by-product profile from limestone-gypsum desulfurization. Rather than producing gypsum that may require paid disposal, the process can generate ammonium sulfate with potential commercial value.
Turning the Resource Cycle into an Engineering Solution
The practical value of ammonia desulfurization depends on whether the process can be reliably integrated into the plant's existing production system.
In one project in Hebei, MirShine Group worked with a coke producer on an ammonia-based FGD project using a fiberglass-reinforced plastic (FRP) desulfurization tower. The project was designed to address regional air pollution control requirements in the Beijing-Tianjin-Hebei area.
The significance of this approach goes beyond replacing one absorbent with another. It connects ammonia recovered during coke oven gas treatment with the flue gas desulfurization process, while creating a route for converting sulfur dioxide into ammonium sulfate fertilizer.
Ammonia water continues to be produced every day in the ammonia-stripping section, and sulfur dioxide continues to enter the FGD system. Bringing these processes together makes it possible to use existing plant resources more effectively and establish a more integrated approach to industrial air pollution control.
For coke plants, the question is no longer only how to meet emission limits. It is also whether existing production and environmental protection systems can work together to reduce operating costs and improve resource utilization.
The ammonia is already there. The opportunity lies in putting it to work where it can deliver greater value.