Hydrogen Sulfide (H2S) Scrubbers: Principles, Types, Costs, and Maintenance

Author: Nikulin V, Head of Engineering

The operation of an H2S wet scrubber relies on the physicochemical interaction between the airflow and a fluid absorbent. Contaminated stream enters the purification unit and passes through a layer of liquid, typically an alkaline solution, which efficiently absorbs the contaminant. During this contact process, this compound dissolves in the medium and reacts with the absorbent, resulting in the formation of less toxic compounds, such as sulfides or thiosulfates.

The airstream, depending on the design of the H2S scrubber unit, flows through a zone of turbulence, packing, or nozzles, where its distribution and contact with the liquid are optimized to maximize absorption efficiency. The H2S-free air is then discharged through an outlet, while the absorbent, saturated with reaction products, is sent to a regeneration or disposal system. To enhance the effectiveness of wet setups, additional stages of purification or absorbent circulation may be implemented.

Sodium hydroxide or sodium carbonate solutions are commonly used as neutralizing agents in a hydrogen sulfide caustic scrubber. These reagents effectively absorb the contaminant, resulting in the formation of non-toxic sulfides or sulfates. In some cases, ammonia or lime water is employed, particularly in methods that require recycling or regeneration of the absorbent. Alkaline neutralizing agents provide a high level of filtration at low operational costs.

It is worth noting that water scrubber H2S configurations are significantly less effective at removing the pollutant compared to their alkaline counterparts. The solubility of the substance in water under standard conditions is approximately 2.6 g/L, which greatly limits its absorption and results in a low purification efficiency. This method may only be suitable for applications involving low concentrations of this compound.

The design of the H2S gas scrubber depends on various factors, including the concentration of the pollutant, the process generating it, the composition of the airflow, the required purification level, and specific preferences for each application. The primary types of the units include wet, dry, vortex, and venturi purifiers, as well as absorption columns with packing.

Let’s take a closer look at a few examples.
A scrubber H2S setups with a floating-bed employs a bed of specialized granules or rings that move freely under the influence of the airstream. Its operating principle is based on the repeated contact of the contaminated mixture with the surfaces of the packing, where the substance accumulates. This packing increases the contact area between the phases, thereby enhancing the cleaning efficiency.

The advantages of this form of the equipment include high throughput and the capability to handle large volumes of gas. However, the floating-bed necessitates regular replacement or cleaning of the packing, which can increase operational costs. It is also important to note that this type of the devices requires a stable incoming airflow and may be less effective during sharp fluctuations in flow rate.

This design of hydrogen sulfide gas scrubber could be further enhanced with a Venturi tube, integrating two cleaning mechanisms to improve efficiency. The Venturi tube facilitates preliminary moisture and turbulent mixing of the airstream with the absorbent, after which the mixture enters the column with floating-bed. This setup allows for deeper filtration due to the increased contact area and extended vapor retention time within the system.

The advantages of this model include an even higher degree of a purification while effectively handling substantial volumes and maintaining stable operation under varying conditions. However, the complexity of the design may lead to increased costs, as well as higher maintenance and operational expenses.

In situations where a small H2S scrubber is necessary, horizontal units can be a suitable option.

In this type of equipment, the airflow flows horizontally through a layer of packing. This design minimizes the overall height of the unit, facilitating installation in spaces with height restrictions. The fixed-bed provides the required depth of contact between the phases. While these cleaners are easier to maintain, they do have limited capacity when handling high loads.

Chemical scrubber H2S configurations commonly use the following reagents: sodium hydroxide, sodium carbonate, lime, potassium hydroxide (less frequently), hydrogen peroxide, mono- and diethanolamine, iron chloride, copper chloride, and ammonia solution.

The caustic scrubber H2S systems (utilizing NaOH, Na₂CO₃, KOH, and Ca(OH)₂) is the most commonly employed option in industry. It delivers high efficiency in removing the substance due to the active reaction of the reagents with the contaminant. This type of devices can function effectively across a wide range of the pollutant concentrations, making it versatile for various industrial processes.

However, a meticulous pH control procedures is crucial to prevent equipment corrosion and maintain efficiency. The formation of by-products, such as sulfides, requires proper disposal. Additionally, neutralizing agent replacement is necessary during operation, which contributes to increased operational costs.

The operation of an amine scrubber H2S system relies on the chemical reaction between the contaminant and ammonia in an aqueous environment. Ammonia's high solubility in water (33 g/L) makes it a suitable reagent for this application.

The primary advantages of ammonia solution are its low expense and the potential for further processing of reaction products, such as NH₄HS and (NH₄)₂SO₄. However, free ammonia, which inevitably evaporates from the scrubbing fluid, may necessitate additional purification. Ammonia methods are more commonly used in facilities with less stringent emission purity requirements or where integrated procedures for recycling reaction products are implemented. The aforementioned ammonium salts can be utilized as components in fertilizer production. This ability to repurpose cleaning by-products sets the amine scrubber for H2S removal apart from many other methods, which often generate waste requiring safe disposal.

The H2S scrubber price is influenced by several key factors. The size and type of the selected device play a significant role in determining the cost, as each requires different design approaches and material quantities. Additionally, the materials used in construction, such as corrosion-resistant metals and plastics, also affect the overall price.

Moreover, the complexity of the control system is an important factor, incorporating automatic sensors and control panels for adjusting purification parameters. The type of agent used—whether alkali, ammonia, or other substances—affects operational outlay and is a crucial consideration when evaluating an H2S scrubber cost. The most economical options include lime, sodium carbonate, and sodium hydroxide (up to $400 per ton). In contrast, potassium hydroxide, ammonia solution, hydrogen peroxide, and amines represent more expensive alternatives, with prices ranging from $600 to $1,200 per ton.

Additional expenses may arise from the necessity to filter by-products and dispose of waste. Installation and commissioning costs include expenses related to on-site setup, logistics, and start-up activities. Maintenance requirements and the frequency of reagent replacement also significantly influence long-term expense. Consequently, the overall price of an air purifier can vary widely based on these factors, which are unique to each specific case. There is no single universal hydrogen sulfide vapor scrubber that is equally effective in all conditions.

It’s worth noting that multiple air filtration units are sometimes employed in series. This strategy is particularly advantageous for handling high or variable concentrations of the pollutant or complex compositions. Each device in the series has a specific function; for instance, the first one removes the bulk of the contaminant, while the subsequent ones further reduce the residual concentration to acceptable levels. This approach allows for the use of different absorbents at each stage, optimizing the process for specific conditions. It also alleviates the load on individual purifiers and extends the lifespan of the equipment.

Choosing an H2S scrubber manufacturer with a proven track record can significantly boost the reliability of your purification practice. As luck would have it, our reputation is indeed well-established—after all, we check it daily, and so far, we’ve never been disappointed in ourselves!

If you still have questions about your facility's emission control, don’t hesitate to reach out for a free consultation. And if you decide to request H2S scrubber quotes, make sure to provide detailed specifications about your facility's airflow rates and contaminant levels. Our engineers will be ready to tailor the perfect solution just for you.