PULP AND PAPER INDUSTRY
EVAPORATORS AND CONCENTRATORS are used to evaporate chemical liquor during the chemical recovery process of chemical pulping. The chemical pulping processes are the kraft, soda, sulfite, or semi chemical process. The kraft process, also known as the sulfate process, uses sodium hydroxide as the process chemical and is the most common form of pulping. The cooking liquor is known as black liquor.
Evaporators may be falling film plate, falling film tubular, rising film tubular, or multi-effect MVR. The first three types of evaporators use only steam, and either the AIROL® 120H875 or the AIROL® 430H125 mist eliminator is used for chemical recovery black liquor evaporation applications for pulp dissolving/papermaking and lignin production, and will return the highest efficiency, as explained below.
Evaporators customarily are used successively in series known as multiple effect evaporators with decreasing temperature and pressure from one effect to the next. The vapor boiled off in one effect is used to heat and boil the liquor in the next effect, and only the first of the vessels at the highest temperature requires an external source of heat. This process maximizes steam economy. CTI mist eliminators at the back end of each effect prevent droplets of concentrated liquor from being conveyed with the outlet steam to the steam chest of the following effect where it could foul the steam side of the following heat exchanger and contaminate its condensate.
Efficiency typically is measured by the amount of sodium carried with the steam into the next effect or downstream condenser. The carry-over is affected by the mist eliminator inlet liquor rate, total dissolved solids in the black liquor, the pressure (resulting velocity), and the style of chevron. In vertical flow applications, 30-40 ppm sodium in condensate following separation is not uncommon, and in horizontal flow, 10-30 ppm sodium is not uncommon.
Because falling film plate type evaporators have lower exit steam velocity off the plate edges, larger droplets are formed, many of which drop out before reaching the mist eliminator. Due to the larger droplets and lower re-entrainment rate, the AIROL® 120H875 vertical flow chevron is the natural choice, providing both an economic and a high efficiency solution.
In tubular evaporators, steam coming out of the tubes is at a much higher velocity, generating finer droplets. In this case, the AIROL® 430H125 is more commonly used. Horizontal flow chevrons are selected for both falling film and rising film tubular evaporators because:
- They are more fouling resistant,
- They can handle higher liquid rates, and,
- They achieve higher efficiency.
The AIROL® 430H125 is sometimes chosen as a more conservative and efficient option for falling film plate evaporators as well, where a shorter and less expensive evaporator is desirable.
When debottlenecking is a concern, or when retrofitting an existing evaporator with insufficient space for an internal mist eliminator, an external in-line mist eliminator, such as the AIROL®430H125 or AIROL® 440H125 is the solution. (See Technical Bulletins, White Papers, Evaporator De-Bottlenecking PDF.)
CTI mist eliminators are installed worldwide in hundreds of evaporators and concentrators.
LIME KILN SCRUBBERS are used in paper mills to produce quicklime from carbonates as part of the chemical recovery process in the causticizing section to convert green liquor from the recovery boiler to white liquor before the liquor is used in the digester to chemically break apart the wood into fiber and chemicals.
High temperature is used in the lime kiln and, depending on fuel source, S02, some HCL, and calcium particulate is driven off. A venturi scrubber followed by a cyclonic separator, cross flow mist eliminator, or vertical flow chevron mist eliminator is used for liquid separation. Often a cyclonic separator will have a vertical flow chevron mist eliminator just beneath the outlet with online provisions for washing out the mist eliminator's soluble and insoluble particulate.
Chevron mist eliminators are used instead of mesh due to their fouling resistance. The AIROL® 120H and AIROL® 130H series vertical flow chevrons, as well as the AIROL® 430H125 horizontal flow chevrons, are commonly used for these applications. The horizontal AIROL® 430H125 has better fouling resistance since drainage is across the gas flow rather than against the gas flow, as in vertical mist eliminators. Vane spacing and number of passes are selected based on the required performance and allowable velocity.
NON-CONDENSABLE GASES (NCG), also known as total reduced sulfur compounds (TRS), are malodorous and flammable. NCGs can be concentrated (CNCG), Dilute (DNCG), or Stripper Off-Gas (SOG). Sources stem from digester degassing, digester blow, reactors, evaporator surface condenser vents, off-gas stripping, smelt tank venting, and other process areas of the mill. The gases are collected and incinerated in the waste wood boiler, recovery boiler, lime kiln, or incinerator.
In addition to reduced sulfur compounds, the gases contain organic compounds such as methanol (MEOH) and turpentine, as well as considerable saturated water vapor. By collecting these gases, most of the pollutants can be removed and burned, and the stripped condensates can be reused in the brown stock washing area and/or make-up water for the causticizing area. Prior to burning, all of the condensed water vapor must be removed. This generally is accomplished through a horizontal flow mist eliminator within a flanged in-line transitional housing designed for full vacuum and 15 psig. The selected chevron is either the AIROL® 430H125 or AIROL® 430H-1-750.
RECOVERY BOILER SCRUBBER - Scrubbers can be installed for particulate removal and/or for direct contact cooling (heat recovery). Typically, mist eliminators for these applications require vertical flow chevrons that follow either packed bed direct contact cooling sections and/or venturi scrubbers. Most frequently the selected chevron is from the AIROL®120H series with vane spacing selected based on the available area and/or the required efficiency. The AIROL® 120H875, a 2-pass chevron with 7/8” vane spacing, is the most frequently used.
TISSUE AND PAPER MACHINE MIST ELIMINATION AND PLANT AIR CLEANING SCRUBBERS
Paper Machine Mist Elimination - Mist removal systems on the wet end of paper machines are used for both plant maintenance purposes and to reduce the contact between dust and high humidity. Since there also are dust, fiber, and some paper collected, the system generally uses a venturi scrubber with cyclone separator, and a final horizontal flow 2-stage mesh coalescer and chevron (AIROL® 120H).
Plant Air Scrubbers - During the manufacturing of tissue, dust is generated after the drying step. As the sheet moves through the various production steps (calendar, slitting and winding operations), dust and fiber will be dislodged from the sheet. To reduce fire risk and improve mill appearance, ventilation systems are added with pick-up points at all sources, terminating at a venturi scrubber with 3-stage separation: cyclone separator, AIROL® 120H875 vertical flow chevron and AIROL® FLOWMAX 320-1 mesh polishing mist eliminator integrated into one vessel. Scrubber bleed-off water is recycled back to the pulper.
GEOTHERMAL POWER INDUSTRY
WELLHEAD FLASH SEPARATION - Salt water or brine in the reservoir rises to the surface of the production well pipe as pressure becomes lower and lower, along with resulting flashed steam. The liquid brine can comprise as much as 60% of the mass of liquid at the surface, with the remaining 40% steam. Separation occurs in a wellhead cyclonic separator designed for what is still a high pressure and temperature condition in the pipeline. High separation efficiency is required to remove most of the brine to safeguard the downstream steam turbine driving the electric generator. Coastal Technologies offers its AIROL® Vortex Cyclone Steam Separator for high removal efficiency at a low pressure drop. (See Benefits of AIROL® Vortex Cyclone Separators and Scrubbers for Geothermal Flash Applications.)
TURBINE STATION SCRUBBER - A steam scrubber is used just before the steam turbine to remove all the steam that condenses between the up-stream separator and the scrubber. The condensate actually scrubs out any residual brine and impurities trapped in the liquid. The typical scrubber inlet liquid load is anywhere from 96% to 99%, and the typical outlet steam quality is 99.95-99.98%. The turbine scrubber can be of the cyclonic design (AIROL® Vortex Cyclone Steam Scrubber) which has no internals, or it can be of a 2-stage AIROL® design using an inlet coalescer/diffuser followed by a chevron mist eliminator. (See AIROL® Vertical 2-Stage Diffuser and Chevron Steam Scrubber.) The scrubber or vessel can be of either vertical or horizontal orientation.
Vessels for both the wellhead separators and the steam scrubbers are designed and built to ASME Code requirements and are PWHT (Post Weld Heat Treated). Material used is typically SA516-70 carbon steel with corrosion and erosion allowances as necessary. Material used for the internal 2-stage design scrubbers is typically 316L stainless steel, although it can be a duplex stainless steel or 6 moly alloy depending on the brine chemistry.
BRINE/CO2 SEPARATION - In water dominated reservoirs there can be conditions where CO2 and brine is produced at the wellhead. The CO2 must be removed before the brine is delivered to the binary power plant. The brine's heat is used to vaporize a hydrocarbon fluid. The separators used for this application are small diameter AIROL® Vortex Separators, which have heavy-duty internal spin vanes.
OIL & GAS
OIL & GAS: Raw natural gas comes from three types of wells: oil wells, gas wells, and condensate wells.
Crude oil wells, in addition to producing oil, may contain raw natural gas called associated gas, which can exist separate from the crude oil, or may be found dissolved in the oil.
Dry gas wells produce only raw natural gas that does not contain any hydrocarbon liquid. Condensate from dry gas, or non-associated gas, is extracted at the gas processing plant and is referred to as plant condensate.
Condensate wells produce raw natural gas along with natural gas liquids. This gas is referred to as wet gas.
CONDENSATE SEPARATION - Processing plants separate oil from gas, and purify raw natural gas by reducing contaminants such as water, carbon dioxide (CO2), hydrogen sulfide (H2S), nitrogen (N2), helium (He), and various non-methane hydrocarbons. Non-methane gases, such as ethane (C2H6), propane (C3H8), normal butane (n-C4H10), isobutene (i-C4H10), and pentanes (C5+) contain a higher content of heavier hydrocarbons. These are collectively referred to as natural gas liquids (NGLs). Hydrocarbon condensate or water separators, as well as intermediate compressors, are common between the gas processing plant and its delivery points. A separator may be either a two-phase: separating gas from liquids; or, a three-phase: separating gas, oil, and water.
Hydrocarbon condensates in a water emulsion generally are not an issue due to their low natural solubility in water. On the other hand, condensates can be used to help clean produced water from oil (heavy oil and water have close specific gravities) and the hydrocarbon condensates can be used to "sweep" up the produced oil from the oil water mixture. The feedstock mixture of gas, liquid condensates and water is routed to one or more production separators that use pressure differentials to cool the wet natural gas and to separate the oil and condensate. In general, gas condensates have a specific gravity ranging from 0.5-0.8. Gas takes up a much larger volume than its equivalent mass of oil, so a pipeline sized for liquid flow will be under-designed if some of the liquid flashes into gas, resulting in excessive velocities and pressure drop. This often is the result of under-sized separators. Separation efficiency is dependent on the difference between the gas density and condensate density.
Sometimes natural gas and oil will separate on its own underground. The natural gas may be cooled below its hydrocarbon dew point at the wellhead to condense a large part of the gas condensate hydrocarbons. Alternatively, the fluid may be sent to an atmospheric storage tank where the pressure is decreased to flash the gas from the liquid. The subsequent hydrocarbons can be sent separate ways for further processing.
The addition of flash tank separator-condensers increase efficiency by absorbing water from the wet gas stream, and by the glycol solution carrying small amounts of methane and other compounds with it. In the past, this methane was simply vented out of the boiler. In addition to losing a portion of the natural gas that was extracted, this venting contributes to air pollution and the greenhouse effect. In order to decrease the amount of methane and other compounds that are lost, flash tank separator-condensers work to remove these compounds before the glycol solution reaches the boiler. Essentially, a flash tank separator consists of a device that reduces the pressure of the glycol solution stream, allowing the methane and other hydrocarbons to vaporize ('flash'). The glycol solution then travels to the boiler, which also may be fitted with air or water cooled condensers that serve to capture any remaining organic compounds remaining in the glycol solution.
Essentially all condensation is removed prior to gas pipeline transport from the plant. Solid particulate and water also are removed to prevent erosion or corrosion to the pipeline. CTI provides OEMs the internals for the separators, which may be AIROL® Mesh pads, chevrons or a combination of the two. Horizontal flow chevrons offer the highest capacity, and allow the vessel diameter to be smaller than a vertical flow chevron will permit. The chevron may be preceded by a wire mesh coalescer if high efficiency is required (99%+ of all droplets 0.6 microns and greater), then coalescing filter cartridges will be required on the back end. Plant output is pipeline-quality, dry natural gas that can be used as fuel (fuel gas).
SOUR GAS SWEETENING uses aqueous solutions of various amines to "sweeten" or remove hydrogen sulfide gas (H2S) and carbon dioxide (CO2) from sour natural gas for subsequent conversion into sulfur. Once the water or liquid hydrocarbons are removed from the sour gas from the refinery in the Knock Out (KO) drum, lean amine in the absorber absorbs and removes the H2S and CO2. The resulting sweet gas exits the absorber through a sweet gas KO drum and is directed to the refinery fuel gas system. The rich saturated amine from the bottom of the absorber goes to a multi-phase separator, where the light hydrocarbons are flashed out of the amine, and heavy hydrocarbons are separated. CTI internals for the knock out drum are the AIROL® 440H-1 in horizontal or vertical orientation, or a vertical flow AIROL® Mesh mist eliminator.
PROCESS STEAM GENERATION - Power boiler steam drums store the steam generated in boiler water tubes and, with the help of mist eliminators, act as a phase-separator for the steam/water mixture. Mist eliminators serve to provide the required steam quality and purity to the plant. While the steam drum is oriented horizontally, the mist eliminators also are commonly installed horizontally – sometimes inclined or tilted. Mesh, chevrons, and a combination of styles can be used for high removal efficiency. Since steam pressure is high, the steam velocity passing through the mist eliminator must be relatively low, and tight vane spacing will be required (1/2" -3/4"). The chevrons used most often are the AIROL® 430H-1-750 or the AIROL® 440H-1-750. The specified efficiency will determine both the chevron spacing and the mesh style (commonly the AIROL® 711 or 911 in 4" to 6" thickness). Chevrons or mesh can be used alone or in combination. If a mesh coalescer is used in front of the chevron in a tilted vertical flow arrangement, it requires only 2" to 3" mesh thickness and may be either the AIROL® 911 or the AIROL® 1111. (See also high capacity / efficiency tilted chevrons AIROL® 130HT-1 FLOWMAX® or AIROL®140HT-1 FLOWMAX®.)
Occasionally, secondary separators for special process applications supplement the primary droplet removal equipment where unusually high quality steam is required. These are special designs and are often provided as a flange-to-flange in-line unit using 2-stage mesh / chevrons (AIROL® 911 or the AIROL® 1111 with AIROL® 430H-1-750 or the AIROL® 440H-1-750).
Once-through steam generators, such as used for oil recovery steam drive systems and steam assisted gravity drainage (SAGD) also can use separators to improve steam quality and reduce the water carry-over.
SO2 SCRUBBING - Recent changes in global regulations require ocean-going vessels to eliminate or significantly reduce SO2 flue gas emissions resulting from the burning of high sulfur bunker fuel oil. The use of tight-space, adaptable, open or closed loop scrubbers serves to fulfill these regulations. High velocity vertical flow mist eliminators permit scrubber vessels to be as small as possible for limited onboard space. In open loop systems, seawater is used to scrub the SO2 in the exhaust gas, forming sulfuric acid. The sulfuric acid is neutralized by the natural alkalinity of the seawater and can be discharged back into the ocean. For closed loop operations, where the buffering capacity of seawater is insufficient for adequate SO2 removal, sodium hydroxide or sodium bicarbonate is added to a freshwater recirculation system. The most common design mist eliminator for either type of scrubber is the AIROL® 130H-1-750 vertical flow chevron. Materials are 316L stainless steel for inland waters, and 6% moly alloy for seawater service.
FLOATING PRODUCTION AND STORAGE (FPSO) VESSEL CAPABILITY - In 2001, CTI was awarded a contract by SPX Dollinger for two (2) cylindrical high capacity chevron mist eliminators to accommodate a full operating range of gas flows for an FPSO. The Shell Nigeria Exploration and Production Company ship "BONGA" is anchored in the Gulf of Guinea, 120km off the Niger Delta extracting 225,000 bbls oil/day and processing 150mm standard m3/day natural gas. The mist eliminators separate water and condensed hydrocarbon liquids from the natural gas leaving a maximum of 200ppm liquids while consuming less than 0.5 psi pressure loss.
AIR INLET LOUVERS / MIST ELIMINATORS - Air inlet mist eliminators prevent seawater mist from entering critical areas, particularly where salt can corrode onboard electronics, such as in the engine room. Additionally, they eliminate atmospheric mist, reducing the formation of mold and other related problems. Mist eliminators can be single stage chevrons (AIROL® 430H-1-750), a 2-stage AIROL® Mesh coalescer followed by a chevron for capturing fine aerosol mists, or a 3-stage unit where the first stage is for bulk water; all can be provided with a weather tight hatch. High operating velocity (30 fps), and low pressure drop, permit small exposed mist eliminator areas to be exposed to the weather.
ADDITIONAL APPLICATIONS INCLUDE:
- Compressor Cooling Fan Inlet to prevent inlet spray water
- Separators for Compressor Interstage Coolers
- Inert Gas Scrubber Mist Eliminators
- Turbine Air Inlet Mist Eliminators – Gas turbines consume large quantities of exhaust gases from a combustion chamber. Turbine vanes are sensitive to erosion by water droplets and by corrosion of fine salt nuclei. Two-stage horizontal flow mist eliminators using inlet mesh coalescers followed by chevron vane mist eliminators provide for operation at high velocity and minimum exposed face area. Installation location is on a protected bulkhead surface. Chevron vanes are vertical with downward drainage across the gas flow with a water sealed drain to the exterior. Materials of construction are typically stainless steel.