Cryogenic Oxygen Plant: Its Applications, Advantages and Salient Features
Oxygen is one of the most essential and plentiful of elements on the planet Earth having numerous industrial and medical applications. However, you might know that oxygen is not readily available in its pure form. It needs to be separated from other gases present in the atmospheric air. There are different methods of producing oxygen like PSA (pressure swing adsorption), membrane separation and cryogenic distillation.
Of all the techniques, cryogenic distillation is the most efficient process for generating high-purity oxygen. In the present write-up, I will discuss about what is a cryogenic oxygen plant, the process of its working, what are the different applications of oxygen, its applications and salient features. And, we also compare how cryogenic distillation technique is better than PSA technique.
In nutshell, a cryogenic oxygen plant is an industrial facility which generates molecular oxygen with purity above 99.5% using low temperatures and high pressures. With air comprising of nitrogen (78%), oxygen (21%), argon (0.9%), and trace gases, the cryogenic distillation process separates air inside a distillation column at cryogenic temperature of around -173°C to produce oxygen and other gases including nitrogen, argon, krypton, helium, and xenon. The process works on the principles of the general theory of the Hampson-Linde cycle of air separation which was pioneered by Carl von Linde in 1895.
Basics of cryogenic oxygen production
The basic steps of cryogenic oxygen production are as follows:
1. Air is filtered and compressed by the compressor which sets up the product pressure as per the demand of the customer. How much air will be sucked in will depend on the oxygen demand of the customers.
2. After being compressed in the compressor, the air moves through a heat exchanger where it is cooled by the outgoing cold product gases. Then, the air passes through a pre-filer and air purification unit (APU) for removal of carbon dioxide, vapor, water and hydrocarbons by adsorption or absorption.
3. Once the air is purified, it is cooled in a main heat exchanger where it attains a near-liquid state. Then, the cold air is put in a turbine thus reducing its temperature and pressure which generates refrigeration in the process.
4. Now, the expanded air comes into a distillation column where it gets separated into oxygen-rich liquid at the bottom and nitrogen-rich vapor at the top. Next, the oxygen is moved into a low pressure column for further distillation to produce high-purity oxygen which is stored in a liquid tank or vaporized for delivery. Similarly, nitrogen is liquefied and stored or vaporized as a by-product. However, there is a separate process for extracting argon and other rare gases from the middle of the column.
5. Subsequently, the reheating of the product gases takes place in the main heat exchanger with the help of the incoming air. Afterwards, the product gases are delivered to the customer through cylinders or pipelines.
Applications of cryogenic oxygen plant in industries
Cryogenic oxygen plant has got numerous applications in various industries including steel, chemical, medical, petroleum, pharmaceutical, food, non-ferrous. Some of the important applications are described below:
Combustion
Oxygen is used for increasing the combustion of fuels including oil, gas, coal, and biomass in power plants, furnaces, kilns, engines and boilers. As a result, the efficiency, output, and environmental performance of the combustion process improve considerably.
Oxidation
Oxygen is used for oxidizing or converting organic or inorganic substances like hydrogen, sulfur, ammonia, carbon monoxide and ethylene into useful products such as hydrogen peroxide, sulfuric acid, nitric acid, carbon dioxide and ethylene dioxide. And, you can find this in chemical reactors, catalytic converters, and gasifiers.
Gasification
Amongst its many applications, we see that oxygen is used for gasifying biomass, coal or waste into a synthetic gas, which is used as a fuel or feedback for chemicals. This is done in gasifiers where oxygen is made to react with carbonaceous material at high temperatures and pressures.
Oxy-fuel cutting & welding
Another important application of oxygen is oxy-fuel cutting and welding where it is used to cut and weld metals like iron, steel, aluminium and copper. This is done by creating a high-temperature flame with a fuel gas, such as acetylene, propane, or hydrogen. It finds applications in torches, plasma cutters, and burners.
Medical
As you might be aware oxygen is used extensively in the medical industry. It is used to treat patients suffering from low oxygen levels such as those with cardiac diseases, respiratory diseases, trauma, or poisoning. Also, it is used to provide life support in artificial ventilation, anesthesia, hyperbaric chambers, and extracorporeal membrane oxygenation (ECMO).
Biomedical
As for use of oxygen in biomedical industry, it is used for culturing cells, tissues, and organs in bioreactors, bioprinters, and biobanks. Besides, it is also used for sterilizing sterilize medical devices, equipment, and implants by using ozone or plasma.
Food & beverages
In the food and beverage sector, use of oxygen include preservation and enhancement of the quality , flavor, color, texture and shelf life of food and beverage products including fruits, fish, vegetables, meat, juice, beer and wine. Moreover, it is also used for aerating and carbonating drinking including soda, water, and sparkling wine.
Advantage of cryogenic oxygen plant over other methods including PSA oxygen plant
There are many advantages of using cryogenic oxygen plants over other methods of oxygen generation including PSA technique. Some of the best advantages are discussed below:
High purity
Cryogenic oxygen plants have the capacity to generate oxygen with more than 99.5% purity, which meets the requirements of applications needing high purity oxygen. Other methods such PSA oxygen plants can only produce oxygen with 90–95%, which might not meet specifications of customers needing high quality oxygen.
High efficiency
High efficiency is a salient feature of cryogenic oxygen plants which operate with low energy consumption ranging from 0.4 to 0.6kWh per Nm3 of oxygen. Certainly, it I lower than energy consumption of other methods such PSA oxygen plants consuming 0.8 to 1.2 kWh per m3 of oxygen. It helps in cutting down the operating cost and environmental impact of oxygen production process.
High Reliability
LOX plants are manufactured to function for long periods of time needing minimum maintenance and downtime. Other technologies available in the market such as PSA O2 plants which need frequent regeneration and replacement of the adsorbent material , which impacts cost of maintenance and the risk of failure.
High flexibility
O2 plants working on cryogenic distillation process can produce oxygen with different purities and pressures as per the specifications of customers. And, cryogenic O2 plant or LOX plant can also generate other gases such as nitrogen, argon, and rare gases as by-products, which can be sold to other customers or used for different purposes.
Salient features of oxygen plant
There are many salient features that unique to cryogenic oxygen plants and are not found in other methods such as PSA plants. Some of the important features are discussed below.
Coldbox
Coldbox is an important component which contains the main heat exchanger, the turbine, and the distillation column. It is designed to maintain low temperatures and high pressures needed for the cryogenic process. And, it is fitted with pressure gauges, temperature sensors, safety valves and flow meters to monitor the process parameters.
Compressor
It is a device that is used for compressing the atmospheric air to the desires pressure for cryogenic separation process. It is operated either by an electric motor or a gas turbine and it is cooled by water or air. Moreover, the compressor is fitted with valves, filters, lubricators and intercoolers to maintain the quality and efficiency of the compressed air.
APU (air separation unit)
APU is a component of the plant which purifies the compressed air by eliminating carbon dioxide, water vapor, and hydrocarbons. It is made up of a molecular sieve adsorber , which does the work of adsorbing impurities on the surface of the zeolite materials. Moreover, the APU is also fitted with a heater that regenerates the adsorber by desorbing the impurities. And, it can regulate the adsorption and regeneration cycles through valves, sensors, and controllers.
Storage tank
It is industrial equipment made for storing liquid oxygen produced by the cryogenic separation process. The storage tank is manufactured with stainless steel and it is insulated by vacuum or perlite. Besides, it has valves, sensors, and controllers to maintain the liquid level, pressure, and temperature of the liquid oxygen.
Vaporizer
It is an important component of the cryogenic air separation plant which vaporizes liquid oxygen for delivery to the customer. And, it has valves, sensors, and controllers to regulate the flow rate, pressure, and temperature of the gaseous oxygen.
Reference: Universalboschi.com, Wikipedia, oxygen-plants.com
