Production




Composition of dry atmospheric air



Without oxygen we would die in a matter of minutes. Many people at work and sometimes at home use oxygen gas in cylinders.

Oxygen gas is the second most common component of the Earth's atmosphere, taking up 20.8% of its volume and 23.1% of its mass (some 1015 tonnes).

Uptake of  Oxygen (O2 ) from the Air is the essential purpose of respiration, so oxygen supplementation is used in medicine. Treatment not only increases oxygen levels in the patient's blood, but has the secondary effect of decreasing resistance to blood flow in many types of diseased lungs, easing work load on the heart. Oxygen therapy is used to treat emphysema, pneumonia, some heart disorders (congestive heart failure), some disorders that cause increased pulmonary artery pressure, and any disease that impairs the body's ability to take up and use gaseous oxygen.

Treatments are flexible enough to be used in hospitals, the patient's home, or increasingly by portable devices. Oxygen tents were once commonly used in oxygen supplementation, but have since been replaced mostly by the use of oxygen masks or nasal cannulas

History of 
Oxygen separation from Air

By the late 19th century scientists realized that Air could be liquefied, and its components isolated, by compressing and cooling it. 

Oxygen was liquified in stable state for the first time on March 29, 1883 by Polish scientists from Jagiellonian University, Zygmunt Wróblewski and Karol Olszewsk

In 1891 Scottish chemist James Dewar was able to produce enough liquid oxygen to study. The first commercially viable process for producing liquid oxygen was independently developed in 1895 by German engineer Carl von Linde and British engineer William Hampson. Both men lowered the temperature of air until it liquefied and then distilled the component gases by boiling them off one at a time and capturing them.

 Two major methods are employed to produce 100 million tonnes of O2 extracted from air for consumptions annually. The most common method is to fractionally distill liquefied air into its various components, with N2 distilling as a vapor while O2 is left as a liquid.

 
Industrial Fractional Distillation  Columns

Fractional distillation is the most common form of separation technology used  in air separation, producing liquid oxygen, liquid nitrogen, and highly concentrated argon.

Fractional distillation is also used in petroleum refineries, petrochemical and chemical plants, natural gas processing and cryogenic air separation plants.

In most cases, the distillation is operated at a continuous steady state. New feed is always being added to the distillation column and products are always being removed. Unless the process is disturbed due to changes in feed, heat, ambient temperature, or condensing, the amount of feed being added and the amount of product being removed are normally equal. This is known as continuous, steady-state fractional distillation.

Industrial fractional distillation is typically performed in large, vertical cylindrical columns known as "distillation or fractionation towers" or "distillation columns" with diameters ranging from about 65 centimeters to 6 meters and heights ranging from about 6 meters to 60 meters or more. The distillation towers have liquid outlets at intervals up the column which allow for the withdrawal of different fractions or products having different boiling points or boiling ranges. By increasing the temperature of the product inside the columns, the different hydrocarbons are separated. The "lightest" products (those with the lowest boiling point) exit from the top of the columns and the "heaviest" products (those with the highest boiling point) exit from the bottom of the column.

 

Air Separation Unit (ASU)

An air separation plant separates atmospheric air into its primary components, typically nitrogen and oxygen, and sometimes also argon and other rare inert gases.

There are various technologies that are used for the separation process, the most common is via cryogenic distillation. This process was pioneered by Dr. Carl von Linde in the early 20th century and is still used today to produce high purity gases. The cryogenic separation process  requires a very tight integration of heat exchangers and separation columns to obtain a good efficiency and all the energy for refrigeration is provided by the compression of the air at the inlet of the unit. In addition to the cryogenic distillation method there are other methods such as Membrane, Pressure Swing Adsorption (PSA) and Vacuum Pressure Swing

Adsorption (VPSA), which are typically used to separate a single component from ordinary air. Production of high purity oxygen, nitrogen, and argon as used for Semiconductor device fabrication requires cryogenic distillation, though. Similarly, the only viable sources of the rare gases neon, krypton, and xenon is the distillation of air using at least two distillation columns. Cryogenic ASU's are built to provide nitrogen and/or oxygen and often co-produce argon where liquid products (Liquid nitrogen "LIN", Liquid oxygen "LOX", and Liquid argon "LAR") can only be produced if sufficient refrigeration is provided for in the design. 

Written Procedures for Filling Oxygen Cylinders




Great care must be taken when filling oxygen cylinders due to the inherent dangers, some of which can be fatal. This is why the task should only be performed by specialized medical professionals (specifically Respiratory Therapists), by auxiliary medical professionals (paramedics and firefighters with special training) or those working for medical supply companies who are qualified.

Proper Storage of H Cylinders

  • All oxygen cylinders should be stored in a clean area at room temperature and in a vertical position to keep particulate matter from accumulating around the neck or valve opening. The valve opening should be capped. To "crack" the H cylinder to check pressurization, be sure the cylinder is upright; point the valve opening away from your body and anyone near. If a regulator is already attached to the valve opening, open the valve slowly at first to pressurize the regulator or you may damage the device. Do not use any tool to open an H cylinder but do so by hand. If the valve won't open, the tank is faulty.
    Medical Cylinders must have hydrostatic tests performed on them every five years. The date of every test is etched directly onto the bottle. Before filling cylinders, check to be sure they are not due for testing.
    Note: most H cylinders used in hospitals are filled from a liquid oxygen storage decanter.

Before Filling  HP Cylinders

  • Check the valve opening for any debris and clear any away (this is usually accomplished by simply "cracking" the cylinder forcefully and briefly if any pressure remains within); if debris cannot easily be removed, tag it as OOS (Out of Service) and report the cylinder's number to the FAO (Food and Agricultural Organization).
    Inspect the cylinder for damage, corrosion, illegal repairs or improper markings. Examine the valve and regulator, if any; be sure they are up to specs and in good condition.
    If unsure of the procedure or something happens that you don't expect, stop the procedure and contact your supervisor or other qualified person before continuing. The potential for explosion makes this a very dangerous task if not performed properly.


    • Filling a Cylinder from Other HP Cylinders (Trans-Filling)

    • Connect the fill valve of the storage unit to the cylinder; tighten by hand alone. Keeping the cylinder upright, place it in a shielded container if one is available.
      Start filling the empty bottle from a cylinder that has a higher pressure. Open the valve slowly. Once the cylinder valve is fully open, open the fill valve, but only partially, allowing a slow rate of fill (a rate not exceeding 200 PSI per minute, as registered on the pressure gauge) to avoid rupturing the empty bottle or the fill line. You will hear a hissing sound that will stop when the pressures are equalized.
      The filling cylinder should never become hot to touch; this indicates too fast a fill rate, though it isn't unusual for the bottle to become slightly warm. If the bottle becomes too warm, close the fill valve and allow it to cool. Remember Boyle's Law: as a warm gas cools within a confined enclosure, pressure will decrease. Try to keep the filling cylinder as cool as possible.
      Once the pressure between the tanks equalizes (hissing stops), follow the same steps in reverse to unhook from the first filler bottle and attach the fill valve to the next cylinder with a higher pressure than the one being filled. Repeat this process until the cylinder is filled to 2000 psi.
      When done with these steps, close the valve on the filled cylinder, then open the bleed off valve on the cascade line. If using a shield, it is safe to open it at this time and disconnect the fill valve from the recharged bottle.
      Cover the cascade valve opening with a plastic cap and store it safely, then fill out the Compressed Air Cascade Usage Chart at the filling station. Before fastening the regulator to the filled bottle, inspect the valve opening for debris. Hand tighten the regulator in place, aim the valve away from you or anyone else and slowly open the valve to check for leaks; check the gauge reading to see if it jibes with the gauge at the filling station. If not, report to your supervisor that the fill gauge may require recalibration. Shut the valve; bleed the pressure from the regulator and remove it from the cylinder, then store the cylinder properly.
      Note: Filling the cylinder to its capacity is not possible with trans-filling.

    Filling a Cylinder from a Liquid Oxygen Storage Tank (Decant Filling)


    To prevent static electricity sparking, rubber soled shoes are required. Due to excessive and rapid freezing likely with liquid decanters, heavy gloves should be worn. Stricter guidelines may call for the use of overalls, eye and ear protection as well. There should be no open flames or smoking within at least 200 feet of the filling station.

    Connect the fill valve of the liquid storage unit to the cylinder; tighten by hand alone. Keeping the cylinder upright, place it in a shielded container if one is available. If there is a metal shield, secure the top before filling begins.

    Most hospital liquid oxygen storage tanks have no shielded area, but are kept a safe distance from populated areas in case of cylinder explosions, which are very rare but possible.

    The filling procedure is basically the same, except that the filler line is equipped with a bleed off valve and should be vented in an open area. Once filling begins, watch for leaks in the line and valves. If any occur, stop the filling procedure before tightening connections or fire may result.

    Storage

    Oxygen can be separated by a number of methods, including chemical reaction and fractional distillation, and then either used immediately or stored for future use.
     
    1. Liquid storage — Liquid oxygen is stored in chilled tanks until required, and then allowed to boil (at a temperature of 90.188 K (−182.96 °C)) to release oxygen as a gas. This is widely used at hospitals due to their high usage requirements, but can also be used in other settings. See Vacuum Insulated Evaporator for more information on this method of storage.
    2. Compressed gas storage — The oxygen gas is compressed in a gas cylinder, which provides a convenient storage, without the requirement for refrigeration found with liquid storage. Large oxygen cylinders hold 6,500 litres (230 cu ft) and can last about two days at a flow rate of 2 litres per minute. A small portable M6 (B) cylinder holds 164 or 170 litres (5.8 or 6.0 cu ft) and weighs about 1.3 to 1.6 kilograms (2.9 to 3.5 lb). These tanks can last 4–6 hours when used with a conserving regulator, which senses the patient's breathing rate and sends pulses of oxygen. Conserving regulators may not be usable by patients who breathe through their mouths.
    3. Instant usage — The use of an electrically powered oxygen concentrator or a chemical reaction based unit can create sufficient oxygen for a patient to use immediately, and these units (especially the electrically powered versions) are in widespread usage for home oxygen therapy and portable personal oxygen, with the advantage of being continuous supply without the need for additional deliveries of bulky cylinders.

    Storerooms should be of fire-proof construction and so designed that in the event of fire, the cylinders are easily removable.

    Storerooms should be well ventilated, top and bottom, and must never be below ground level.
    Light fittings, as well as all electric switches in stores containing acetylene, Handigas or other flammable gases, should either be of the flame-proof type, or should be placed outside thebuilding lighting the interior through fixed windows. 'NO SMOKING - NO NAKED LIGHTS' symbolic signs, should be posted in the area of the store.

    Handigas cylinders stored inside a building on an industrial user's premises should be limited to a total mass of 19kg per 600m3 of building space with a total maximum of 100kg.
    Where Handigas is stored in bulk, reference should be made to SABS 087 Part 1 and Part 3. Since these may be updated from time to time, it is important to ensure that reference is made to the latest issue.
    Afrox Limited has a specialised department for the installation of gas distribution systems, storage vessels, etc.

    Handigas cylinders exceeding a total capacity of 19kg should not be installed or kept inside a private home or a place of business frequented by the public. Cylinders must be kept cool, and should be protected from sunlight, rain, frost, wet soil and corrosive conditions. If cylinders have to stand in the open, they should be protected from the rays of the sun. Do not use tarpaulins or any other cover which comes in direct contact with the cylinders as a protection against the sun.

    Full or empty combustible gas cylinders should be kept apart using 'ful' and 'empty' notices to prevent confusion and mistakes.

    The valves of empty cylinders should always be firmly closed to prevent 'breathing'. If a cylinder is found with the valve open, close it and attach a note stating this fact, e.g.

    WARNING - CYLINDER VALVE LEFT OPEN WHEN CYLINDER EMPTY'.

    This will ensure that moisture and purity tests are carried out before the cylinder is refilled. Oxygen should not be stored with flammable gases such as acetylene and Handigas. Acetylene and Handigas cylinders should NOT be stacked horizontally, but should always be stored in an upright position.
    Oxygen cylinders may be stacked horizontally provided that they are firmly secured at each end to prevent rolling.

    If cylinders are exposed to heat, the pressure of the gas content will increase, and a dangerous situation may arise.Therefore, store all cylinders well away from sources of heat such as furnaces, stoves, boilers and radiators as well as potential fire hazards.

    Oil and grease will ignite violently in the presence of oxygen and if the latter is under pressure this may result in an explosion. Cylinders and fittings should be kept away from overhead shafting, cranes or belts.
    Prevent dirt, grit of any sort, oil or any other lubricant from entering the cylinder valves and store cylinders well clear of any corrosive influence, e.g. battery acid. Do not lubricate the valve spindle.

    Do not smoke, wear oily or greasy clothes, or have any naked light or fire in a place where compressed gases are stored.

    Transportation & Handling


    People who do not get enough air naturally have to use supplemental oxygen to help their breathing and improve their quality of life. Oxygen gas that's stored in cylinders is either compressed oxygen gas or liquid oxygen. Follow the government guidelines for transporting these cylinders to be safe

    1.Read the manufacturer's instructions located on the label of the cylinder. It contains detailed instructions and precautions that must be taken when handling the oxygen cylinders.

    2 Wash your hands of any oil or grease. You should not handle oxygen cylinders with slippery hands

    3.Check each cylinder to make sure it is free of leaks and cracks before you load it onto your vehicle. Inspect the area around the valve and the pressure relief device. If the cylinder contains any dents, is gouged or pitted, then you should not handle it. .

    4.Place a protective valve cap on each cylinder. Secure and store cylinders in a portable cylinder rack or cart designed to transport cylinders. These carts have locking mechanisms that safely keep cylinders in place in an upright position. The cylinders should not block any aisles or exits. Most importantly, store away from sources of heat and potential sparks.

    5.Sit the cylinder tanks in an upright position in crates or boxes if you're transporting oxygen tanks in the cargo compartment of a vehicle. These gas cylinders must be also be free from movement. 

    6.Remove all cylinder from your vehicle immediately once you reach your destination.


    Liquid Oxygen
    Oxygen is an abundant element, and as a gas it comprises more than 20 percent of earth's atmosphere and is necessary for most types of life to survive. However, pure oxygen is a very rare element, since most of earth's oxygen is naturally mixed with other gases and water vapor. But like all elements, the oxygen in the atmosphere is only in a "gas" state, and under the proper conditions it can be converted into a liquid. This requires extremely low temperatures--low enough for the oxygen atoms to lose enough energy and collapse into a fluid state. In this form, oxygen is a cryogenic liquid, with a boiling point below -297 degrees Fahrenheit.

    Dangers

    • Liquid oxygen has many useful applications, but it is very dangerous to handle. Oxygen is naturally a corrosive agent, and in its liquid form great care must be taken while handling it, since it is both an intense oxidizer and has freezing properties similar to liquid nitrogen. It also facilitates the combustion of substances, causing fires to burn much more easily and more powerfully. This is why liquid oxygen is often used in rocket and jet fuel. This means that allowing outside heat and movement anywhere near the oxygen-charged environment of liquid oxygen can be very hazardous, causing explosions or fires.
    In order to transport liquid oxygen, complex tanks are designed with multiple layers so that no outside warmth can penetrate to the cryogenic liquid. A space is created between the inner tank and the outer tank, and air is pumped out of that space, leaving a vacuum between the tank contained the liquid oxygen and the outer protective shell. These tanks are heavily reinforced to prevent cracking or leakage in case of accidents.

    Liquid oxygen is less expensive to transport, since it takes up less room, but it usually needs to be converted back to gas to be used. Tanks are not filled completely with liquid oxygen. There is always a warmer space into which the oxygen immediately evaporates. This means that that top part of an oxygen tank is always filled with pure oxygen gas. A series of valves and tubes allows intermittent access to this top area, letting the gas flow away and be replaced by more evaporating oxygen.

    Safety Practices

    • Oxygen tanks are required to be inspected before they are transported, and the tanks must meet guidelines that specify safety precautions, temperatures and piping designs. They should always be stored in an upright position, and of course there can be no signs of wear or corrosion.

    Uses

     
    Oxygen therapy is the administration of oxygen as a medical intervention, which can be for a variety of purposes in both chronic and acute patient care. Oxygen is essential for cell metabolism, and in turn, tissue oxygenation is essential for all normal physiological functions.

    High blood and tissue levels of oxygen can be helpful or damaging, depending on circumstances and oxygen therapy should be used to benefit the patient by increasing the supply of oxygen to the lungs and thereby increasing the availability of oxygen to the body tissues, especially when the patient is suffering from hypoxia and/or hypoxaemia.

     Indications for use 

    Oxygen is used as a medical treatment in both chronic and acute cases, and can be used in hospital, pre-hospital or entirely out of hospital, dependant on the needs of the patient and the views of the medical professional advising.

    Use in chronic conditions

    A common use of supplementary oxygen is in patients with chronic obstructive pulmonary disease (COPD),the occurrence of chronic bronchitis or emphysema, a common long term effect of smoking, who may require additional oxygen to breathe either during a temporary worsening of their condition, or throughout the day and night. It is indicated in COPD patients with PaO2 ≤ 55mmHg or SaO2 ≤ 88% and has been shown to increase lifespan.

    Oxygen is often prescribed for people with breathlessness, in the setting of end-stage cardiac or respiratory failure, advanced cancer or neurodegenerative disease, despite having relatively normal blood oxygen levels. A 2010 trial of 239 subjects found no significant difference in reducing breathlessness between oxygen and air delivered in the same way

    Use in acute conditions

    Oxygen is widely used in emergency medicine, both in hospital and by emergency medical services or advanced first aiders.

    In the pre-hospital environment, high flow oxygen is definitively indicated for use in resuscitation, major trauma, anaphylaxis, major haemorrhage, shock, active convulsions and hypothermia.

    It may also be indicated for any other patient where their injury or illness has caused hypoxaemia, although in this case oxygen flow should be moderated to achieve target oxygen saturation levels, based on pulse oximetry (with a target level of 94–98% in most patients, or 88–92% in COPD patients).

    For personal use, high concentration oxygen is used as home therapy to abort cluster headache attacks, due to its vaso-constrictive effects.

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