Desulfurization plant - Gazpack

Sulfur as an element is ubiquitous. In the universe, it ranks 10th inprevalence; on the earth, it comes in fifth. It is found in vitamins, amino acids, the earth&#;s crust, and virtually every plant and animal. There are myriad uses of sulfur in industry and agriculture, including herbicides, pesticides and fertilizers. Needless to say, it is a critical element in nature and in the economy. Nevertheless, when present in certain chemical compounds and mixtures, sulfur does not play well with others. These compounds can be hazardous to health; damaging to the ecology; and corrosive to many materials utilized for industrial purposes. The organisms and matter where these dangerous compounds are found must be subject to the desulfurization process.

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What Does That Mean?

The desulfurization meaning is actually two-fold: it could refer to removing elemental sulfur at the molecular level or, alternatively, extracting sulfur compounds from chemical mixtures. On its own, sulfur can be extricated from subterranean deposits by melting it through the injection of water heated above the boiling point. Once melted, the sulfur is piped out to the surface. Simple enough. What, though, about those dangerous compounds that find themselves in diverse compositions like natural gas, biomass and petroleum, for instance? What does desulfurization look like when the element is bonded to others?

Natural Gas

Natural gas formations exist all over the world. The largest deposits are located in the Middle East, the Russian Federation and Europe. In North America, natural gas is most abundant in Texas, Oklahoma, New Mexico, Wyoming, and Louisiana. In the United States, over 50 percent of homes are heated by natural gas and this fuel accounts for 24 percent of energy use overall. Natural gas is also a constituent ingredient of many paints, plastics and even medicines. Propane gas &#; popular with avid grillers and barbecue enthusiasts &#; is also derived from natural gas.

Natural gas is often retrieved from its earthen deposits in the same manner as petroleum &#; through drilling or hydraulic fracturing. Sometimes a &#;horse head&#; pump is employed to draw both natural gas and oil to the surface. This resource is found in shale formations, coal beds and sandstone. Once the gas is drawn from its source, it is transported via 300,000 miles of pipeline to locations throughout the U.S., eventually available to customers. Before this lengthy trip, however, the gas must be treated to remove the hydrogen sulfide (H2S) and carbon dioxide (CO2).

The desulfurization of natural gas is necessary for two very important reasons. The H2S that is present is not only toxic to workers and consumers but it is also detrimental to the very pipeline networks that deliver the fuel. At its worst, it can induce respiratory failure, coma and even death to those exposed. Meanwhile, it can quickly oxidize the metal interiors of natural gas pipelines, thereby damaging their safety and overall efficiency. Therefore, natural gas needs treatment at a desulfurization plant soon after its retrieval from wherever it is deposited.

If hydrogen sulfide presence surpasses 5.7 milligrams per cubic meter of natural gas, the gas passes a threshold from user-grade to &#;sour&#; gas. Under such a circumstance the gas is ordinarily run through a tower or column that contains amine, i.e. a derivative of ammonia. The amine solution absorbs the H2S compound as the gas stream passes through, leaving a purer effluent natural gas in its wake. The amine solution is available for further use over many cycles of H2S removal. This procedure for H2S removal is performed in the vast majority of occasions when hydrogen sulfide absorbtion is necessary.

Biogas

Essentially, biogas is the methane (and CO2) that gets released from organic matter under anaerobic &#; or oxygen-deprived &#; conditions. This can take place naturally, as at the core of a compost heap or landfill, or it can be induced by human technology, i.e. engineered anaerobic digesters. Absent oxygen, bacterial micro-organisms operate on the organic material, breaking it down so that biogas is released from the solids that had retained it. The material is as diverse as sewage, food waste, compost, wastewater, rotting vegetation and animal manure. Once captured, the biogas powers combustion engines which, subsequently, charge electrical generators. Biogas can provide energy to vehicles, farms, neighborhoods and even public transit systems.

Still, biogas, too, has an H2S problem, the very same problem evident with natural gas. The public health threat and infrastructure impairment are equally real with biogas production. Fortunately, biogas desulfurization is available by means of two distinct methods.

1. Wet de-sulfurization &#; can be further broken down into three versions:

• Chemical absorption &#; is most akin to amine sweetening with natural gas. Besides amine, straight ammonia and carbonate serve as alternate solvents for the attraction and intake of hydrogen sulfide.
• Physical absorption &#; combines components of solvent with a drop in pressure to separate the H2S from the biogas.
• Wet oxidation &#; uses a weak basic solution to absorb and oxidize the H2S, thereby removing the elemental sulfur from the compound.

2. Dry de-sulfurization &#; rather than using a solvent or solution, dry de-sulfurization utilizes powder/particle agents to treat the biogas. Doing so minimizes the possibility of corrosion in the biogas tank. In general, this method works better when sulfur content is on the low side.

Once properly purified, biogas is an unsung hero of renewable fuels. Not only is it environmentally friendly and cost-effective, it answers a large part of the seemingly eternal waste management question.

Flue Gas

Hydrogen sulfide is not the only problematic sulfur compound in energy production. Sulfur dioxide (AO2) is emitted from exhaust flues at energy plants that burn fossil fuels and facilities that incinerate solid wastes. In nature, SO2 is released when volcanoes erupt. On a smaller scale, it is emitted whenever a match is lighted. Implicated in acid rain, SO2 is a major air pollutant that affects habitat livability and the survival of various plant and animal species.

How does flue gas desulfurization work? As with the categories noted above, there are multiple ways to do this. One such procedure is wet scrubbing. This involves an alkaline absorbent slurry &#; limestone, lime or even seawater &#; that is sprayed directly on the gas stream or pooled to receive the stream. At other times the slurry is converted to powder by means of hot gas. When the flue gas makes contact with the particles, a similar reaction removes the sulfur molecules. This method is known as spray-dry scrubbing. Other means of flow gas desulfurization are employed depending on sulfur content and related factors. Like atmospheric CO2 scrubbers, these treatments isolate the SO2 from the flue gas stream before it is released into the air.

The atmospheric residue desulfurization process helps to keep toxic particulates from doing damage to ecosystems and the air we breathe. The various methods heretofore mentioned take place in an atmospheric residue desulfurization unit where not only sulfur dioxide, but nitrogen oxides and other particulates are captured and isolated.

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How Is Sulfur Retrieved from Compounds?

Many of the agents responsible for neutralizing H2S can separate the sulfur from its compounds. However, research demonstrates that an iron oxide sold sponge &#; i.e. wood shavings infused with iron, or ferric, oxide &#; is effective in hydrogen desulfurization by first absorbing the H2S, and then converting ferric oxide into ferric sulfide. The ferric sulfide subsequently reverts to ferric oxide after releasing elemental sulfur.

Adsorptive Desulfurization

Adsorptive Desulfurization is an innovative technique that has transformed the way we address the presence of sulfur in gas streams. At Gazpack, we pride ourselves on leveraging cutting-edge technology such as Adsorptive Desulfurization to remove sulfur from a variety of gases. This process involves adsorbents like zeolites, activated carbons, or metal-oxides that selectively trap sulfur compounds, resulting in a cleaned gas stream. Importantly, Adsorptive Desulfurization provides a more efficient, economical, and environmentally friendly alternative to conventional desulfurization methods, particularly when dealing with gas streams containing low concentrations of sulfur. 

In Summary

Energy sources with less CO2 emission than traditional fossil fuels promise greater energy independence and a cleaner environment. Yet even these gases have contaminants that require removal before they are burned for electrical generation or combusted for vehicular performance. The good news is that technology (desulfurization plant) provides for the removal of sulfur compounds before the energy is consumed.

What Are the Effluent Limitation Guidelines (ELG)?

The combustion of fossil fuels to power manufacturing and refining facilities occurs across a wide range of industrial sectors. Fossil fuel plants power chemical and oil refineries, as well as those facilities that produce cement, paper, glass, steel, iron, copper, and other metals. The SO2 gases emitted as a result of that process are a primary contributor to acid rain and has long been regulated by every industrialized nation in the world due to their harmful effects on human health and the environment. In the U.S., ELG rules regulate wastewater discharges from coal-fired power plants and IGCC power plant wastewaters utilized in flue gas air pollution control systems or solid waste handling systems. Flue-gas desulfurization was an important development to meet environmental challenges.

Flue Gas Desulfurization Processes

The process of FGD is designed to absorb the sulfur dioxide in the flue gas before it is released. This is accomplished through either a wet or a dry process.

Dry FGD

In the process of dry scrubbing injection systems, lime is used as a reagent to react and remove gaseous pollutants. There are two common dry methods, the dry injection system and spray drying systems. Each process injects lime into flue gas to remove SO2. A dry injection process injects dry hydrated lime directly into the flue gas duct, whereas the spray dry system injects atomized lime slurry into a separate vessel. Both methods yield a dry final product, collected in particulate control devices for further treatment.

Wet FGD

The process of wet scrubbing typically utilizes an alkaline-based slurry of lime to scrub gases. A shower of lime slurry is then sprayed into a flue gas scrubber, where the SO2 is absorbed into the spray and becomes a wet calcium sulfite. One by-product of that sulfite is it can be converted to salable gypsum. Wet scrubbing provides high-efficiency sulfur dioxide removal capacity, in addition to reducing any scaling potential.

FGD Wastewater Treatment

The circulating water used during the wet scrubbing process ends up with many contaminants and pollutants, and the composition can vary significantly, plant to plant, influenced by factors such as the coal and limestone composition. In order for operating conditions to be properly maintained, this FGD wastewater needs to be discharged constantly from the scrubber system through a purge stream consisting of contaminants from coal, limestone, and the makeup water. The water is typically supersaturated with gypsum, is highly acidic with high concentrations of total dissolved solids (TDS) and total suspended solids (TSS), chlorides, fluorides, nitrites and nitrates, along with trace metals such as arsenic, mercury, selenium, boron, cadmium, and zinc.

Flue gas desulfurization wastewater can be effectively and efficiently treated using large filter presses or large vacuum belt filters for very large sludge production. Recess chamber filter presses are used effectively in coal-fired power plants to separate the solids from liquids in the purge stream. The FGS sludge dewatering process results in formation of large volumes of dry filter cake for proper disposal in a landfill. In some instances, additional treatment of the wastewater may be necessary if, for instance, lower levels of nitrates or selenium are required.

FGD sludge dewatering is only one step &#; yet an important step &#; in the overall FGD process. But when it comes to dewatering, proper filter media selection will play a critical role in effectively treating the wastewater from the purge stream. This will be a big contributor to the overall process of eliminating SO2 from the flue gases.

Micronics&#; liquid/solid separation experts will happily help with all aspects of a filter press solution for coal-fired power plants including proper selection of high-quality filter press cloth.

Did You Know&#;Micronics can also supply filter belt cloth for horizontal vacuum filters.

We are proud of our role in providing engineered filtration solutions that help with environmental protection and ensure compliance with ELG Guidelines, including keeping acid rain in check.

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