This plant has a maximum capacity of 40,000 scfh (666 scfm), and can easily be ‘turned down’ to 32,000 scfh (533 scfm). • The estimated power usage: 0.76 KWH/ 100 scf
Approximately 1600 SCFM air enters intake F-10, where dust and debris are removed prior to entering the first stage of compression of CP-11. Air pressure is increased at each of the three stages of CP-11 and passed through tube and shell heat exchangers to remove heat of compression and free water from the air stream. Condensate is then collected and drained out of the system through condensate traps. The final air from CP-11 is 100 PSIG, saturated air at approximately 95F.
The air from CP-11 is then passed to chiller R-15, where it is further cooled to 50F using mechanical refrigeration. This drop in temperature causes more moisture to condense into free water, which is drained through condensate traps.
The chilled 100 PSIG air enters the PPU bed which is on the adsorption step. The materials in this vessel strips the air of moisture, CO2 and most hydrocarbons. These components must be removed prior to being cooled to cryogenic temperatures to avoid ice and dry ice accumulation inside the coldbox piping, column and heat exchangers. These contaminants are trapped in the desiccant material until the regeneration step, when hot waste gas (40% O2/60% N2, 250 SCFM) is admitted to flow through the material in the opposite direction of the air, causing the contaminants to exit the system with the waste gas. The heat cycle then ends and the bed is cooled and prepared to go into adsorption service when the cycle repeats. After adsorption, the clean dry air passes through a dust filter to avoid passing powdered material into the coldbox.
The moisture, CO2 free air, still at approximately 50F now enters the coldbox. Nitrogen product and Oxygen waste gas exiting the main heat exchangers N21/N31 flows counter to the incoming air, transferring the heat from the air to the exiting, cold gases. Because of this, the air is cooled to just a bit warmer then liquefaction temperature and the outgoing gases are warmed to almost the incoming air temperature of 50F. A small portion of the cold air is passed through liquefier N43, where it is cooled further and liquefied before entering high pressure column along with the remaining incoming air.
Properties of Air
Since the cryogenic process described below is based on the physical properties of air, these properties need to be discussed briefly.
Approximate condensing/vaporizing temperature of major components of air at atmospheric pressure:
Oxygen -297FArgon -305FNitrogen -320F
There are two basic principles that must be understood to understand the distillation process:
1. Since Nitrogen becomes a liquid at -320F and Oxygen only has to be -297F to liquefy, liquid Nitrogen will condense the Oxygen out of the air in a distillation column.2. As pressure increases, the condensing/vaporizing temperature also increases. This is why the crude liquid Oxygen covering N74, which is at 25 PSIG, is cold enough to liquefy the Nitrogen gas at the top of N67 at 75 PSIG. This is where the down flowing reflux comes from.
Distillation Column System
As the air enters the High Pressure Column N67, it rises through the distillation trays where it contacts the down flowing reflux liquid from the condenser N74. Since the upward flowing gas is contacted by the colder downward flowing liquid, some of the Oxygen is stripped and joins the reflux liquid, thus decreasing the O2 content of the gas and increasing the O2 content of the liquid. This process repeats on each of the many distillation trays until the upper portion of the column contains very little O2 and the liquid at the bottom of the column is approximately 40% oxygen. This liquid is transferred into the condenser N74 where it provides the cooling for the production of the reflux liquid.
The liquid crude Oxygen in condenser N74 warms as it is providing the cooling for reflux production. Because of this, the O2 rich liquid is caused to boil and vaporize to a gas. This gas passes through liquefier N43 and is warmed a bit before entering Expander X-35.
Waste gas enters expander X-35 at approximately 28 PSIG and -256F and exits at approximately 5 PSIG and -286F. This pressure and temperature drop are caused by the waste gas forcing the turbine wheel to turn and transferring power to pump oil at the other end of the common shaft. This transfer of energy causes the gas to cool in the same way that a pneumatic impact gun becomes cold while transferring pressure energy to turn lug nuts on a wheel. All of the coldbox refrigeration comes from X-35 in this way. The colder, exiting gas from X-35 then flows back through liquefier N43 where it is slightly warmed, then it flows out through the main heat exchangers N21/N31 where it provides much of the cooling to the incoming air stream. The waste gas leaves the coldbox just slightly cooler than the incoming 50F air. A portion of the waste gas is used as regeneration gas for the PPU and the remainder vents to atmosphere through vent silencer N17.
The Nitrogen gas at the top of column N67 is purified to less than 1 PPM O2 by the distillation process. This high purity, cold gas leaves the column and is slightly warmed in liquefier N43 before flowing through main heat exchangers N21/N31 where it provides the remaining cooling to the incoming air stream. A small stream of product N2 is withdrawn after it exits N31 cold exchanger to provide a balancing flow for the heat exchanger system, which flows to X-35. The product Nitrogen exits the coldbox just slightly colder than the incoming 50F air.
Product Compressor CP-71
Product compressor CP-71 increases the N2 product pressure from 75 PSIG to 130 PSIG. The N2 then passes though a glycol/water heat exchanger to remove the heat of compression to approximately 95F, before flowing to the customer pipeline system.
Pipeline Flow Load Following
The HPN-40 control system includes a load following system, which adjusts air flow to the coldbox based on pipeline usage. This system is designed to minimize power consumption during low usage periods. As Nitrogen consumption decreases, the setpoint to the CP-11 airflow control slowly decreases to a lower setting. As flow increases on the pipeline, the air flow setpoint gradually increases to provide enough air to provide the required product.
• CP-11 Main Air Compressor
CP-11 is a 3 stage centrifugal air compressor manufactured by Cameron compressor. The compressor is driven by a 500 HP 4160 volt Siemens electric motor. This compressor brings air from the atmosphere and compresses it to approximately 100 PSIG. Interstage cooling and condensate removal are achieved by 3 tube and shell, glycol/water cooled exchangers. This unit is fully controlled by the plant control system.
• R-15 Chiller
The R-15 chiller is a package chiller manufactured by Nortec, utilizing high and low side compressors with a glycol/water cooled condenser. Air from CP-11 is cooled to 50F and the condensate is removed by utilizing 2 moisture separators. The coolant charge is HFC Ozone safe. The controls on this unit are on board, with start/stop and alarming integrated into the plant control system.
• D-16 Prepurifier Unit (PPU)
The D-16 PPU system is manufactured by PSB Industries. The unit includes 2 vessels containing activated alumina and mole sieve material to remove moisture, Carbon Dioxide and hydrocarbons from the chilled air stream. The vessels switch between adsorption and regeneration cycles by a sequence of valve position changes, which are controlled by the plant control system. Waste Oxygen is used as the regeneration gas.
The coldbox contains the main heat exchangers N21/N31, liquefier N43, column N67 and the condenser N74. These pieces of equipment cool, liquefy and separate the Nitrogen from the other impurities contained in the atmospheric air. Waste Oxygen exits the main heat exchangers to provide cooling and regeneration gas for the PPU system. The coldbox is controlled entirely through the plant control system.
• X-35 Expander
The X-35 Expander is manufactured by Mafi Trench and provides the refrigeration required to separate the atmospheric gases. Energy from the entering waste Oxygen is transferred to an oil brake, through a common shaft. This energy transfer causes the waste gas to cool approximately 30F. X-35 has a main and stand by oil pump, which starts automatically in case of low oil pressure. This unit is controlled through the plant control system.
• CP-71 Product Compressor
CP-71 Product compressor increases the product Nitrogen pressure to 130 PSIG from column pressure. The compressor is manufactured by Rotoflow Corporation and is a single stage centrifugal unit. CP-71 has a main and stand by oil pump, which starts automatically in case of low oil pressure. This compressor is controlled through the plant control system.
• CT91/92 Cooling System
The CT91/92 cooling system was manufactured by Hydrothrift Corporation and consists of a fin/fan system (CT-92A and CT-92B) which cools 338 GPM of 50/50 glycol/water mixture during typical Winter, Spring and Fall months. When the ambient temperature exceeds 75F, the open cooling tower (CT-91) is utilized to “trim” the closed system to maintain proper operating temperature cooling water/glycol. This system has redundant water and glycol/water pumps, which will start automatically upon low pressure conditions . This system was chosen to avoid any potential of freezing any water during cold weather conditions, considering unattended plant operations. The entire system is controlled by an on board control panel, however, the system is integrated into the plant control system for start/stop and alarming capability.
• F-300 Disposal Vaporizer
The F-300 disposal vaporizer consists of a spray header and electric fan, which starts and stops automatically, based on incoming temperature, to vaporize any liquids that enter it. This unit is controlled by the plant control system.
• HE-965 Derime Heater
HE-965 is a 45 KW electric heater designed to heat 1200 SCFM of air from 50F to 140F for plant derime. The heater is controlled by the plant control system.
Nortec ARC 3000 W Condition: NewMaximum flow capacity: 1800 SCFMInlet Temperature: 95 FInlet pressure: 100 psigAmbient Temp: 95F - 100 FInlet and Outlet connections: 4 inch flangePressure drop: 3.5 - 4.5 psiCondenser: Water CooledCompressor: HermeticRefrigerant: R 404AVoltage: 480 V 3 Ph 60 Hz 32.6 Amps
PSB Industries Model 363P-SP Condition: NewCapacity: 2100 SCFM inlet air at 100 psig, 50 F max.Desicants: 400 lbs activated alumina per tower 1500 lbs mole sieve per towerElectrical panel: NEMA 4 Outdoor non-hazardous locationPower: 480 V, 3 PH, 60 Hz, 48.8 Amps
Mafi-Trench expander / hydrobrake
rebuilt 2010 and not returned to serviceLube oil pump A: 3 HP 480 V 3 Ph 60 HzLube oil Pump B: 3 HP 480 V 3 Ph 60 HzLube Oil Heater: 3 kw 480 V 3 Ph 60 Hz
Type: Rotflow single stage cetrifugalCondition: Rebuilt 2010 and not placed in serviceInlet pressure: 75 psigOutlet Pressure: 130 psigMotor: 100 HP 480 V 3 Ph 60 HzLube oil pump A: 5 HP 480 V 3 Ph 60 HzLube oil pump B: 5 HP 480 V 3 Ph 60 HzLube oil heater: 3 kw 480 V 3 Ph 60 Hz
CT-92A & 92B Fin Fan Systems: Hydrothrift model FEVF35408-68 2 eachDescription: Fin/fan system for cooling 50/50 glycol/water mixture.Condition: New never usedDesign Parameters Flow: 338 Gallons / Min Ambient temp: dry bulb 98 FCool Water Temp: 85 FWarm Water Temp: 101 FLiquid: 50/50 Glycol Water mixPump Head, Feet: 180Power: 460 V 3 Ph 60 HzPumps: Dual Goulds 3656M 30 HPOther: 100 Gallon Vent & Surge Tank CT-91 Trim for CT-91 A, B during hot weather Marley Aquatower Model AQ496K1GAFDescription: 1 cell cross flow cooling tower.Condition: New, Never usedDesign Parameters Flow: 500 Gallons /minWarm Water Temp: 89 FCold Water Temp: 80 FWater entering basin temp: 64 FPumps: Dual Goulds 3656M 15 HPFan: 5 HP 1 speed 460 V 3 Ph 60 HzBasin Heater: 6 kw 460 V 3 Ph 60 Hz
All pipe spools and pipe supports are made and available for installing the plant on a 60 ft by 70 ft pad.
- Nitrogen purity specifications are as follows:
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