The NOx AND SO2 Abatement Technologies

Acid Rain

“Acid rain” is a broad term used to describe several ways that acids fall out of the atmosphere. A more precise term is acid deposition, which has two parts: wet and dry. Wet deposition refers to acidic rain, fog, and snow. Dry deposition refers to acidic gases and particles. About half of the acidity in the atmosphere falls back to earth through dry deposition. The wind blows these acidic particles and gases onto buildings, cars, homes, and trees. Dry deposited gases and particles can also be washed from trees and other surfaces by rainstorms and the runoff water adds those acids to the acid rain, making the combination more acidic than the falling rain alone.

Scientists have confirmed, that sulfur dioxide (SO2) and nitrogen oxides (NOx) are the primary causes of acid rain. About 2/3 of all SO2 and 1/4 of all NOx comes from electric power generation that relies on burning fossil fuels like coal. Acid rain occurs when these gases react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds.. The result is a mild solution of sulfuric acid and nitric acid.

Acid rain (sulfates, nitrates, and ground level ozone – smog) have significant adverse effects on human health (inhalable fine particles), and the environment. Acid rain causes acidification of lakes and streams and contributes to damage of trees at high elevations (for example, red spruce trees above 2,000 feet) and many sensitive forest soils. In addition, acid rain accelerates the decay of building materials and paints, including irreplaceable buildings, statues and sculptures that are part of nations’ cultural heritage. Prior to falling to the earth, SO2 and NOx gases and their particulate matter derivatives, sulfates and nitrates, contribute to visibility degradation and harm public health.

Current Status of SO2/NOx Abatement Technologies

Selective Non-Catalytic Reduction (SNCR)

SCR (NOx) The SCR technology utilizes injection of ammonia (NH3) into the flue gas in the presence of a catalyst. The catalyst promotes reactions that convert NOx to nitrogen and water at higher removal efficiencies and lower flue gas temperatures than required for SNCR.

SNCR technology is probably most advanced in implementation. It can reduce NOx emissions by 30 to 50% without significant impactsonunitperformance InSNCR,ammonia(NH3)orureaisinjectedintothefluegastoreduceNOxtonitrogenandwater.

The technology was initially demonstrated in boilers fired by oil or natural gas, but the use of SNCR in coal-fired boilers is presently under way. The technology has been demonstrated in 15 utility-scale boilers in the United States and Europe (especially in Germany and Austria).

NOx emissions in the flue gas are converted into elemental nitrogen and water by injecting a nitrogen-based chemical reagent, most commonly urea (CH2CONH2) or ammonia (NH3; either anhydrous or aqueous). Because the highest NOx reduction is achieved at temperatures between 870 and 1,200°C (1,600 to 2,200°F), the reagent is introduced at the top and backpass of the boiler. Multiple injection locations may be required, especially in case of cycling units; different injection locations are used as the unit operates at a reduced load.

The following technical issues remain to be addressed: Ability to satisfactorily minimize deposition of ammonium bisulfate on the air heater baskets, which plugs them, especially at boilers burning high-sulfur coal (above 2-2.5%) Ammonia contamination of the ash; ammonia is odorous at concentrations as low as 20 ppm.

Based on market quotes, the cost of retrofitting a boiler with SNCR is S$10 per 20/kW, whereas incorporating SNCR in a new boiler is US$5 to 10/kW. This difference is caused by the cost associated with modifying the existing boiler to install the reagent injection ports. The operating costs associated with the reagent, auxiliary power, and potential adverse O&M impacts are usually on the order of 1 to 2 mills/kWh. Two to five weeks of outage are required to retrofit a boiler with SNCR.

This technology is considered suitable for developing countries that require NOx reduction above and beyond what is achieved by low-NOx burners. The suitability and deployment of the combined SO2/NOx control processes in developing countries should be assessed though after they have been demonstrated and commercialized in industrialized countries (3 to 10 years, depending on the process).

In general the existing abatement technologies have a number of drawbacks: 1.Complex, large volume and costly installations (made of inox), expensive catalyzers, high temperatures and/or high pressure environments, expensive materials (ammonia, hydrogen), 2. Typically, low emissions burners are being installed before the actual abatement technology which increases the total costs. 3.they do not eliminate entirely the NOx (SNCR: 30 – 50%) 4. the NOx abatement from exhaust gases with concentrations below 0.5% is economically prohibitive.

Numerous processes attempting to provide a cost-effective alternative to the combination SCR-wet FGD are under development that combine SO2 and NOx removal to reduce the design and operating complexity of these systems. Some of these processes are in the development stage and are not available commercially yet. The advantages and disadvantages of six selected categories are provided in the following table.


The Lion Alternative Energy NOx AND SO2 Abatement Technology

Lion Alternative Energy PLC (Lion) has developed a technology for the abatement of NOx and SO2 which has a lower capital investment and lower operating cost than the other existing technologies, it eliminates 100% of the pollutants, and in addition, it generates income from the sales of Nitric Acid and Sulphur Dioxide generated in the process.

Main accomplishments of the new Lion abatement technology

Accomplishes total NOx and SO2 abatement (as opposed to the other existing technologies which accomplish only a partial abatement since a total abatement would be economically prohibitive).

Can recover NOx and SO2 from low concentration gases (below 0.5%). Can be applied to both high sulphur coal and low sulphur coal combustion.

It is recovering two components of the exhaust gases wasted by all other technologies: the heat content and the SO2 and HNO3 content.

Generates income from sales of recovered SO2 and HNO3.

No ammonia, platinum, natural gas, oil or coal are needed as raw materials.
Substantial reduction in the volume (and weight) of equipment (leading to lower shipping costs).

Uses a large percentage of plastic components that leads to both a reduced equipment cost and less corrosion in operation.

Oxygen is not required by the process, air is sufficient for oxygenation.

Released gases are innocuous, (do not contain O2) and could be used in the ammonia industry or as protection inert gases in processes where the contact between processed materials and oxidating substances must be avoided.

Reduced energy consumption by using the heat content of exhaust gases, operating at normal pressure and reduced movement of gases in the system.

The Lion technology could be used:

1. For the abatement of NOx and SO2 from exhaust gases released by the power generating (and other) industries with simultaneous production of revenue generating HNO3 and SO2 or

2. In the chemical industry for the low cost production of SO2 and HNO3 – 68% or fumans. (it is estimated that the HNO3 production cost using the Lion technology is less than USD 50/t, while the market price of HNO3 is over USD 300 / t and the estimated world production surpasses 60 Million ton/yr.

The Lion NOx AND SO2 Abatement Installation

The new technology is an absolute innovation, which, for the first time, after Berkelund and Eyde allows the binding of nitrogen from exhaust gases (or the atmosphere as the case may be) with a very low energy consumption and without the use of additional raw materials (ammonia, platinum, natural gas, oil or coal).

The Lion technology is based on a selective reversible chemosorption process, using special compounds. (complexing solutions).

The installation has two stages, each using a specific complexing solution (adsorbent compound) which reacts with SO2 and respectively NOx and form complex combinations whose stability can be thermally controlled. The complex substances formed at low or moderate temperatures, are decomposed at high temperature, releasing the SO2 and NOx in pure state.

The selective chemosorption process is using very efficiently the high heat content of the flue gases, this leading to a low energy consumption. Also, the special design scrubber structures have very low hydraulic resistance to the flow of gases and allow a high speed transfer gas – liquid, with further energy savings.

Flue gases with SO2 and NOx content are directed by blower into the cooler I , where they release heat for the operation of the ammonia absorption machine, then to cooler II where steam is produced, and then to cooler III where they reach the temperature required by the absorption process of NOx in scrubber I.

In scrubber I, flue gases flow in counter-current with the complexing solution I, at 0 – 6 iC, being circulated through an external cooler with ammonia from the ammonia machine. A part of the complexing solution collected at the base of scrubber I , is sent to a steam heat exchanger, where NOx is desorbed and then, oxidated with air into nitrogen dioxide, and absorbed in scrubber for the production of commercial nitric acid. (HNO3) Complexing solution I, less the NOx, is cooled and recycled to scrubber I through the correction device .

The flue gases, cleaned of the NOx content, are transferred from the top of scrubber I to the bottom of scrubber II , where they release the SO2 to the complexing solution II, which is circulated in a closed system with heat exchangers that produces commercial SO2.

The flue gases with a content of less than 0.1 ppm NOx and less than 0.25 ppm SO2 are finally released into the atmosphere.

The recovered SO2 and respectively NOx in concentrated state, are further processed into commercial products, through known processes.

The research for the technology has been finalized by Lion and tested at the level of 3,000 t / yr of HNO3 in Eastern Europe.



Nitric Acid (HNO3), Adipic Acid (C6H10O4) and Nitrous Oxide (N2O)

The nitric acid (HNO3) is an extremely important chemical. The main use of nitric acid is in making ammonium nitrate (NH4NO3) used as an agricultural fertilizer. The nitrate fertilizers have provided great benefits to mankind in increasing the food yield from otherwise poor soils.

Another important use (15%) is the manufacture of various explosives, such as trinitrotoluene (TNT), nitrocellulose, nitroglycerin, and RDX and PETN (the last two being components of Semtex). Nitroglycerin (the explosive component of dynamite) is made by adding nitric and sulfuric acids to glycerol under very carefully controlled conditions. Also, NH4NO3 is an ingredient in many gunpowder recipes, and is an important explosive in its own right Nitric acid is also used as an oxidizing agent in the manufacture of nylon and in making dyes.

The commercial nitric acid is typically a solution of 52% to 68% nitric acid in water. Fuming nitric acid is a commercial grade containing 90% HNO3. This grade is often used in the explosives industry. Red fuming nitric acid, or RFNA, contains substantial quantities of dissolved nitrogen dioxide (NO2). An inhibited fuming nitric acid (either IWFNA, or IRFNA) can be made by the addition of 0.6 to 0.7% hydrogen fluoride (HF) which creates a metal fluoride layer that protects the metal tanks.

HNO3 is produced chiefly by oxidation of ammonia (the Ostwald process). Small amounts are produced by the treatment of sodium nitrate with sulfuric acid. The existing technology for the production of nitric acid releases NOx emission. (based on measurements at a DuPont plant 2 – 9 grams of nitrous oxide emissions are released per kilogram of nitric acid manufactured)

The market price per ton of HNO3 68% is USD 300 – 450 / ton and the estimated annual world production is over 60 Million ton (Europe 20 million ton). Most of this tonnage is used captively and the merchant market probably involves only about 10% of the total. International trade has little impact on the nitric acid balance.
Western Europe, the United States, the former USSR and Eastern Europe dominate the market. Together, these regions accounted for 74%, 79% and 79% of world capacity, production and consumption, respectively.

World demand for nitric acid will continue to be largely dependent upon demand for solid ammonium nitrate fertilizer and nitrogen fertilizer solutions that incorporate ammonium nitrate. The trend toward the use of solid urea, rather than solid ammonium nitrate fertilizers, which has restricted growth in the use of ammonium nitrate, (which has in turn restricted growth in nitric acid consumption) is expected to be offset by the anticipated growth in liquid fertilizers containing ammonium nitrate.

Adipic Acid (C6H10O4)

An additional product which could be created as a result of the Lion abatement technology is the Adipic Acid, used primarily in the production of nylon fibers and plasticizers for polyvinyl chloride and polyurethane resins, lubricants, insecticides, and dyes. Annual production is estimated at 1,500 million mt / yr and the market price (99.7%) at USD 1,000 / ton – 1,400 / ton.

The current industrial processes for the manufacturing of adipic acid involve oxidizing a ketone-alcohol mixture with nitric acid, which releases NOx (0.3 mt of NOx for every MT of adipic acid produced). The Lion technology, in addition of realizing the adipic acid at a substantially lower cost, reduces also the NOx emissions of the process.

Nitrous Oxide (N2O) is a colorless, odorless non flammable naturally occurring gas that is used as an anesthetic and analgesic, pharmacologic agent, additive to fuels to increase available oxygen in combustion, food aerosol in the preparation of whipping cream.

Sulfur Dioxide (SO2)

Sulfur dioxide is a highly toxic, colorless, nonflammable gas in liquid form when under pressure, and it dissolves in water. SO2 could be further transformed in sulfuric acid monohydrate or oleum.

Direct uses include: pharmaceutical aid and antioxidant, food preservative, sanitizing agent for food containers and fermentation equipment, foods stabilizer, moisture control agent, flavor modifier and texturiser. It is used for the production of sodium sulfite (cellulose – paper fabrication), aliphatic sulphonic acids (additive and detergents), sodium pirosulfite (dyes, glucose, initiate polymerization), sodium tiosulfate (bleaching agent in the textile and paper industry, tanning of hides), sulfochloride polyethylene (special polymer) as chlorinating agent (sulfuryl chloride, sulfuryl fluoride used in fine organic syntheses and pharmaceutical industry). Indirect uses include: sulfur trioxide (sulfonatation, detergents, pesticides, synthetic resins), sodium sulfate (detergents, cellulose, glass, cement, artificial silk), sulfonic acid, (pesticides and explosives), inorganic acids, various sulfates – ammonium, aluminum, barium, copper, zinc, magnesium. Current market price for Sulfur dioxide liq. bulk f.o.b. works is USD 300 – 500 / ton

Sulfuric Acid (H2SO4)

Sulfuric acid is a colorless oily liquid soluble in water with release of heat. It is corrosive to metals and tissue. Long term exposure to low concentrations or short term exposure to high concentrations can result in adverse health effects from inhalation.

About 65% of world sulfuric acid is produced from elemental sulfur and 13% from pyrites and the balance from other sources (mainly smelter gases). Over the years, the volume produced from elemental sulfur has increased at the expense of pyrites. Phosphate fertilizer companies produce sulfuric acid mainly from elemental sulfur. Sometimes they also participate in the merchant sulfuric acid market, selling excess acid at the gate or supplementing their requirements with purchased acid, typically by product acid.

International trade involves approximately 5% of world sulfuric acid production. Increased recovery of byproduct sulfuric acid at smelters (as a result of emissions limitation regulations) has had a significant impact on the industry, leading to increased trade in sulfuric acid (since byproduct producers are not necessarily located near acid markets) and forcing some sulfur burning plants to close. One portion of the sulfuric acid business that has grown as a result of environmental restrictions is the portion that regenerates sulfuric acid.

Sulfuric acid is the world’s largest volume industrial chemical. The production of phosphate fertilizers, especially wet-process phosphoric acid, is the major end use market for sulfuric acid, accounting for nearly 60% of total world consumption. The balance is used in petroleum refining, iron and steel production and a variety of industrial applications. Annual estimated world production is 200 million ton (US 35.8 million t, Europe 19 million t, Russia 8.6 million t) with an estimated fob value for 98 % grade of USD 200 – 280/t.

The Asian Market
China – a World Problem for Acid Rain Pollution

China has gone through an industrialization process in the past 20 years that many developing countries needed 100 years to complete. China=s double digit economic growth is dependent to a large extent on coal power plants, and the Chinese economy can be called a Acoal fueled economy@. China ranks 3rd in the world in coal reserves with 114.5 billion tons (after US with 246.6 billion and Russia with 157 billion) but ranks first in both coal production and consumption with approx. 2 billion tons per year. To make it worse, the sulfur content of the Chinese coal (1.1%) is higher than that of most other countries.

Scientists are recognizing the path of destruction caused by China’s industrial revolution and are concerned that the Chinese are no longer destroying only their own environment, but the pollution generated in China is exported and spread across the planet. Sulfuric Acid and Nitric Acid, formed when SO2 and NOx combine with water vapor in the atmosphere, travel hundreds and thousands of miles and come down to the surface as acid rain. China=s neighbors (Japan, South Korea, India) have raised complaints about acid rains which can be traced back to China=s coal burning. But even as far as the US, scientists say 30% or more of the mercury residing into US ground or waterways comes from offshore, in particular China.

At over 26 million tons SO2 emissions per year China is currently world’s largest SO2 polluter. The country’s factories and power plants emit more SO2 than Europe. Half of China’s 696 cities and counties suffer from acid rain and the polluted air is causing 400,000 estimated deaths each year. The World Bank estimates environmental pollution already shaves off 8 – 12 % of China’s gross national product. Currently, 90% of SO2 emissions and 70% of NOx emissions in China are generated by coal burning, 50% of which is from coal power plants. The current capacity of installed Flue Gas Desulphurization facilities (FGD) is about 53,000 MW, accounting for only some 14% of thermal power installed capacity. China plans to invest in the following years approx. $19 billion in FGD installations and approx. $4.7 billion in annual operating costs according to the State Environmental Protection Agency.

By 2020, installed power generation capacity is expected to be 800,000 MW, of which 75% thermal power and China=s goal is to limit by 2020 the SO2 pollution from power plants to 6-7 million t /year. In order to achieve this goal, the FGD capacity of coal power units needs to reach 350,000 MW nationwide.

The FGD techniques currently operating in China have a 80-95% SO2 reduction efficiency and they include limestone – gypsum scrubbing, rotary sprayed dry process, circulating fluidized bed, electron beam ammonia, seawater scrubbing, LIFAC, etc. Based on technical imports, China is now capable of designing, constructing and operating FGD installations. A large number of small to medium enterprises compete in the FGD installation market. This had as effect the reduction of prices and profit margins in the FGD installations to $25,000-30,000/MW due to: design simplifications (no forced oxidation), use of carbon steel instead of stainless steel in absorbers, cheaper (thinner) manually applied absorber lining, cheap auxiliary components, low labor cost. These factors raise concerns about equipment reliability (40% of completed FGD units are idle due to technical problems), sustainability of low prices and increase in O&M costs.

Most of the world’s megacities (over 10 million residents) are mushrooming in Asia, many of which currently have nonexistent or ineffective air pollution regulations. By 2025, 21 of the world’s 37 megacities will be in Asia. Asia is expected to be a primary market for the Lion abatement technology since the Lion equipment has a substantially lower cost than the already low prices practiced in the Asian markets, it has a higher abatement ratio and it offsets capital and operations costs through the byproducts generated.

Lion could implement in China its emissions abatement program applied to both high sulphur coal and low sulphur coal combustion under strict quality supervision norms and form a marketing subsidiary for the distribution of the sulfuric and nitric acids byproducts.