Chemical Processing Technology Articles

Manufacturers use synthesis gas, or “syngas” for fuel to produce electricity and as feedstock for production of industrial chemicals such as ammonia, methanol, and other hydrogen-rich compounds. Once isolated and purified, hydrogen from syngas is a major component in petrochemicals and oil refining. Syngas itself is a mixture primarily of hydrogen and carbon monoxide, created through the gasification of hydrocarbons in natural gas, coal, petroleum, biomass, and other feedstocks. Virtually all the hydrogen produced in the United States is produced from methane. And the cheapest, most available source of methane is natural gas.   Steam Methane Reforming Steam methane reforming (SMR) accounts for about 95 percent of the industrial hydrogen produced domestically and about half the world’s production. The process begins with the introduction of superheated (1,300 to 1,800 degrees Fahrenheit) steam and natural gas into an array of vertically hanging tubes filled with nickel catalyst. As the mixture flows through the tubes, which are heated externally (the reaction is endothermic), the methane in the natural gas reacts with the water vapor to produce hydrogen and carbon monoxide: CH4 + H2O < ——– > 3H2 + CO Ensuring the feed mixture contains excess steam ensures the maximum production of hydrogen. Plentiful steam also enables the consumption of as much methane as possible. Methane in the product is an impurity and must be stripped from the gas later in the process. Nearly complete conversion of methane has the added benefit of preventing creation of elemental carbon, which can deposit on and foul the catalyst. At present, the most widely used and cheapest method for hydrogen production is the steam reforming of methane (natural gas). This method includes about half of the world hydrogen production, and hydrogen price is about US$ 7 / GJ. Below listed are several well-known companies which provide process technology and engineering of syngas / hydrogen production on the basis of steam reforming. The number in parenthesis shows the units installed worldwide approximately.   Foster Wheeler (100) Lurgi (30) Linde (120) KBR (100) Uhde (60) Praxair (140) Haldor Topsoe (40) Technip (240) CB&I (175)   Water-Gas Shift Reaction Another reason for incorporating relatively more steam than methane in the mixture is to encourage a secondary reaction for the recovery of additional hydrogen. In this process, the mixture passes through another set of tubes of iron-chromium catalyst in a fixed-bed reactor where the molecules in the water vapor are split into oxygen and hydrogen. The hydrogen is collected along with that produced in the SMR process. The oxygen bonds with the carbon monoxide from SMR to make carbon dioxide. CO + H2O < ——– > CO2 + H2 Unlike the primary reaction, the water-gas shift reaction is exothermic, and the energy produced can be captured to partially fuel the steam-heating required in SMR. Pressure Swing Adsorption While steam methane reforming and water-gas shift reactions are quite efficient, complete reaction of methane is impossible because the reactions are subject to thermal equilibrium. This leaves some unreacted methane along with the carbon dioxide from the final product, some unreacted carbon monoxide, water vapor, and other contaminants in the gas mixture. As many operations require virtually pure hydrogen, the pressure swing adsorption process removes these contaminants. This is accomplished by pumping the mixture through cylinders filled with specially treated beads to which the unwanted gasses adhere. Once the pristine hydrogen is pumped out of the cylinders, pressure can be lowered, releasing the contaminants from the beads. They then can be flushed from the chamber. Numerous hydrogen PSA units have been installed worldwide. Leading technology licensors include:   KBR Air Products & Chemicals Linde Praxair UOP Lurgi   Conclusion A modern syngas / hydrogen plant typically has capacity range from 5 MMSCFD to 200 MMSCFD. For a 90 MMSCFD plant, the capital cost to build such a plant is estimated at approximately US$ 55 million nowadays. Average hydrogen production cost is US$ 1.60 per 1,000 standard cubic feet, or US$ 53 million per year to operate a plant of this capacity. This estimate is based on the following utility consumption. Utilities consumption per 1,000 ft3 of contained hydrogen:   Natural gas feed, million Btu LHV 317 Natural gas fuel, million Btu LHV 126 HP export steam, lbs 90 Boiler feedwater, lbs 120 Power, kWh 52 Cooling water, gal 8   Low-cost feedstock and efficient conversion of hydrogen makes steam methane reforming from natural gas the most widely used process for syngas production. Phoenix Equipment sells used hydrogen and syngas plants, and hydrogen purification components that are immediately available for purchase and relocation. Buying a used plant can save you significant capital and drastically shorten the time required to build or expand manufacturing operations.

The manufacturing of nitric acid for use in fertilizers, plastics, dyes, textiles, and other industrial products, has evolved to three industry-standard processes. They all produce acid with 60-68% concentration, and each uses essentially the same nitric acid plant design. The choice between medium- and high-pressure mono and dual-pressure production process often comes down to financial considerations and owner priorities. Nitric Acid Production Technology While nitric acid plant technology has made production more efficient and environmental controls more effective, the process remains the same: Ammonia combustion in the presence of hot air and a platinum/rhodium catalyst creates nitric oxide (NO). Oxidation of the NO creates nitrogen dioxide (NO2). The NO is cooled and compressed as it travels to the absorption tower. The cooling process creates nitrogen dioxide and produces heat, which is recycled for use in other plant operations. Absorption of the NO2 in water creates nitric acid (HNO3). This dilute solution dissolves in the remaining water. The reaction also forms small quantities of NO, which combine with ambient oxygen to reform NO2 and continue the reaction. Modern nitric acid plants are designed to carry out the three chemical processes in a variety of ways, considering initial investment costs, space constraints, feedstock cost, and other factors. The oxidation reaction is more efficient under medium pressure, while the absorption and ultimate production of nitric acid solution works better under high pressure. As a result, three distinct processes have been developed for carrying out the various reactions.   1. Mono Medium Pressure Process Using an uncooled radial compressor to deliver air at 4 to 5 bar abs or an axial flow compressor (5 to 6 bar abs) a nitric acid plant can produce up to 700 tons of nitric acid per day (maximum 65 percent concentration) using a single ammonia combustion unit and a single absorption tower. Production can be increased to 1,000 tons per day with the addition of a second absorption tower. Because the oxidation of nitric oxide into nitrogen dioxide occurs more quickly at lower temperatures, nitric acid plants using mono medium are more efficient than their high-pressure counterparts at this portion of the production process. And because the reaction is exothermic, the mono-medium setup’s ability to maximize energy recovery helps offset operating costs. The compressor can be driven by reusing steam captured during nitric acid production. Or, if steam can be exported for credits, the compressor can be driven by electric motor so all generated steam can be collected for export. 2. Mono High Pressure Process While medium-pressure nitric acid plants optimize the second critical chemical reaction, raising the pressure to 8 to 12 bars enhances the final step. The higher pressure “forces” the nitrogen dioxide (and dinitrogen tetraoxide, which is also produced in the oxidation phase) gas into water. Manufacturers seeking a quick capital often take advantage of this nitric acid plant technology, as a single absorption tower is sufficient to produce up to 1,000 tons of nitric acid per day. The higher pressure also means the burner unit, piping, and other equipment can be made smaller so the plant occupies a more compact footprint, making the initial capital investment less and the road to profitability shorter. 3. Dual Pressure Process As might be surmised, the dual pressure process uses two different pressures during nitric acid production. It uses medium pressure for the compressed air used in ammonia combustion, then compresses to high pressure to optimize absorption. An attempt to capitalize on the best of both mono processes, the dual pressure process can realize up to 1,500 tons per day of nitric acid (up to 70% or higher concentration) with one ammonia combustion and process gas cooler unit installed. Additional units can be added to increase capacity. The lower oxidation pressure also takes less of a toll on the catalyst – a major savings, considering the cost of platinum. Varying the pressure not only extends catalyst life, but also keeps the nitric acid concentration low as it exits the condenser, fostering its absorption into water. Which is the Best Nitric Acid Production Process? All three processes have their place in nitric acid plant design, depending on strategic goals and other factors. Initial investment in medium- and high-pressure mono process plants are generally lower than those required for dual-pressure facilities. Variable costs, however, can run higher, requiring slightly larger quantities of ammonia and taking a greater toll on the catalyst. As a result, mono –pressure nitric acid technology is more prevalent in smaller (900 tons per day and less) plants. Most experts consider the dual-pressure process the best available technology, and most new high-capacity nitric acid plants are designed for dual pressure. Because both technologies are incorporated, a higher initial investment is required, but the greater capacity and lower operating costs help recoup the investment more quickly. Typical Consumption Figures of Modern Nitric Acid Plants The following chart is the comparison of typical consumption figures for steam turbine driven and inline compressor set nitric acid plants, per ton of nitric acid (100%), with NOx content in the tail gas of less than 50 ppm. Plant Type Medium Pressure Process High Pressure Process Dual Pressure Process Operating Pressure (abs.) 5.8 bar 10.0 bar 4.6 / 12.0 bar Ammonia 284 kg 286 kg 282 kg Electricity 9.0 KWH 13.0 KWH 8.5 KWH Platinum, Primary Losses 0.15 g 0.26 g 0.13 g Platinum losses after recovery 0.04 g 0.08 g 0.03 g Cooling water (Δt = 10 k), including water for steam turbine condenser 100 t 130 t 105 t Process Water 0.3 t 0.3 t 0.3 t LP heating steam, 8 bar, saturated 0.05 t 0.20 t 0.05 t HP excess steam, 40 bar, 450 ºC 0.76 t 0.55 t 0.65 t Energy Recovery and Tail Gas Treatment Whichever technology a nitric acid plant uses, each reaction in the production process releases energy, which can be recovered and used throughout the plant. For instance, the air used to oxidize the ammonia must be filtered, compressed and heated. It is possible to obtain nearly all the energy required for these processes by extracting heat from tail gasses. Nitric acid plants must treat the NO, N2O, and NO2 gasses produced throughout the manufacturing process. Both are greenhouse gasses and can do great harm to the environment if not properly neutralized. A variety of technologies exist to make these waste gasses less harmful including: Heating them in the presence of a catalyst to convert NOx to nitrogen Installing additional absorption trays (or a complete additional absorption tower) Cooling weak acid within the absorption tower Attaching molecular sieves to contact tail gasses to return NO for another pass through the absorber Use of liquid alkali, carbonates, or potassium permanganate (wet scrubbers) to pull NO from tail gas to form nitrate salts Leading Technology Licensors Weatherly, a company of Chematur Engineering Group of Sweden; ESPINDESA, a company of Técnicas Reunidas of Spain; Borealis of Austria; Uhde (now ThyssenKrupp Industrial Solutions) of Germany; MECS Technology of USA; KBR of USA; Technip of France. Planning to start or expand a nitric acid plant? Phoenix Equipment buys and sells complete nitric acid plants. Take a look at our current nitric acid plant inventory or if you can’t find what you need, contact us today and one of our plant experts can assist you in finding exactly what you need, no matter which nitric acid production process you are looking for.