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Showing posts with label caustic soda. Show all posts
Showing posts with label caustic soda. Show all posts

Tuesday, August 25, 2015

Production of Caustic soda by desalination of sea water with fresh water as by-product


There is a great deal of misconception about desalination of seawater and the word ‘desalination’ is taken literally as a method of separating fresh water from seawater but not the separation of salt from seawater. The main focus here is only about recovery of fresh water from seawater or from any saline water sources but not salt. In fact separation of salt from seawater is also known as desalination or desalting. The reason for this misconception is because fresh drinking water is in demand and people are concerned only with fresh water and not the salt. There is a huge demand for fresh drinking water all over the world. Increasing population, large scale usage of fresh water by industries, pollution of fresh water by domestic and industrial effluents, failure of monsoon or seasonal rains due to climate change are some of the factors that contributes to water shortage. There is also a demand for water by agriculture industry both in terms of quality and quantity. Bulk of the ground water is used as a main source of fresh water by agriculture industries in many countries. But sea water also contains number of minerals or salts which have greater economic and commercial value. In terms of quantity their presence is small, only 3.5% and the rest 96.5% is fresh water. For example Chemical industries such as Caustic soda and Soda ash plants use salt as their raw material. But they also use demineralized water to dissolve salt to produce brine which is their feed stock. Therefore Chemical plants are the largest users of seawater in terms of salt as well as fresh water. Power plants mainly located on seashore also use large quantity of demineralized or desalinated water for boilers and for cooling towers. Sea is now becoming a great source of fresh water as the inland water supply is becoming scarcer due to dwindling water table by drought or flooding by too much rains, pollution by industries etc. In earlier days seawater was the only source of common salt known as Sodium chloride produced by solar evaporation. Bulk of the salt is till used by this method. Therefore it is logical to locate a chemical plant and a power plant side by side so that seawater can be utilized efficiently. CEWT (Australian company) has developed a new desalination technology called ‘CAPZ desalination technology’ that can generate fresh water as well as Sodium chloride brine simultaneously which is suitable for Caustic soda/Soda ash production. They can integrate such a facility with a skid mounted Chlorine plant of smaller capacities. This plant can generate large volume of drinking water (WHO standard) as a by-product that can be supplied to municipalities and agriculture industries. Locating large scale solar salt pans near such a facility will be a problem because it requires a huge area of arid land with good wind velocity and it takes nearly a year to harvest the salt. Using CAPZ desalination technology one can generate saturated Sodium chloride brine of 315 gpl concentration as well as fresh drinking water directly from seawater. The brine is purified to meet the specifications required by membrane Electrolysis for the production of Caustic Soda. The same brine can also be used for the production of Soda ash using Solvay process. It is no longer necessary to produce brine from solar salt. Solar salt requires vast area of arid land with good wind velocity and least rain fall and large manual labour force to work under harsh conditions; it is a very slow process and takes almost a year to harvest the salt, which is full of impurities and requires elaborate purification process during the production of Caustic Soda. Such purification process generates huge volume of solid waste for disposal. Chlor-alkali industry is one of the most polluting industries in the world. In fact these impurities can be converted into more value added products such as recovery of Magnesium metal or recover of Potassium salts. CAPZ technology is developing a ZLD (zero liquid discharge) desalination process where the effluent containing the above impurities such as Calcium, Magnesium and Sulphates are converted into value added products. By recovering more such salts from seawater one can recover additional fresh water. Therefore desalination of sea water is now emerging as an integral part of Chlor-alkali industry. By such integration Chlor-alkali can become a major player is meeting fresh drinking water of a nation. By careful integration and co-location of a desalination plant, Caustic soda plant, Food and pharmaceutical grade salt plant and a power plant on a sea shore will be a win situation for everybody involved. Let us take a specific case study of setting up a Caustic soda plant, a captive power plant and a desalination facility. A typical skid mounted Chlorine plant will have the following configuration: Capacity of Caustic Soda: 50.7 Mt/day (100% basis) Capacity of Chlorine : 45.00 Mt/day (100% basis) Hydrogen production : 14,800m3/day (100% basis) A typical usage of Vacuum salt for such skid mounted Chlorine plant will be about 76.50 Mt/day with a power consumption of 2.29 Mwhr/Mt of NaOH (100%). A captive power plant of capacity 200Mw will be able to supply necessary power for both Desalination facility as well as Caustic soda plant. The CAPZ desalination facility can supply a saturated sodium chloride brine (315gpl concentration) 245 Mt/day and 9122 m3/day of fresh drinking water from the desalination plant. This water can be used for boiler feed in the power plant. Surplus water can be supplied as drinking water meeting WHO specifications.
The Hydrogen gas the by-product from caustic soda plant with capacity of 14,800 m3/day can be used to generate clean power using a Fuel cell. The power generated from Fuel cell will be about 20 Mwhr/day that can be supplemented for the Caustic soda production thereby reducing the power consumption from 2.29Mwhr to 1.46 Mwhr/Mt of NaOH (100%) By careful integration of a large (ZLD) desalination facility with caustic soda plant and power plant it will be possible in future to generate a clean energy using Hydrogen, a by-product of Caustic soda plant and solar thermal plant to produce chemicals in a clean and environmentally sustainable manner. For further information on CAPZ technology, please contact ahilan@clean-energy-water-tech.com.

Thursday, December 6, 2012

Innovative desalination technology

Seawater desalination is a technology that provides drinking water for millions of people around the world. With increasing industrialization and water usage and lack of recycling or reuse, the demand for fresh water is increasing at the fastest rate. Industries such as power plants use bulk of water for cooling purpose and chemical industries use water for their processing. Agriculture is also a major user of water and countries like India exploit ground water for this purpose. To supplement fresh water, Governments and industries in many parts of the world are now turning to desalinated seawater as a potential source of fresh water. However, desalination of seawater to generate fresh water is an expensive option, due to its large energy usage. However, due to frequent failure of monsoon rains and uncertainties and changing weather pattern due to global warming, seawater desalinations is becoming a potential source of fresh water, despite its cost and environmental issues. Seawater desalination technology has not undergone any major changes during the past three decades. Reverse osmosis is currently the most sought after technology for desalination due to increasing efficiencies of the membranes and energy saving devices. In spite of all these improvements the biggest problem with desalination technologies is still the rate of recovery of fresh water. The best recovery in SWRO plants is about 50% of the input water. Higher recoveries create additional problems such as scaling, higher energy requirements and O&M issues and many suppliers would like to restrict the recoveries to 35%, especially when they have to guarantee the life of membranes and the plant. Seawater is nothing but fresh water with large quantities of dissolved salts. The concentration of total dissolved salts in seawater is about 35,000mgs/lit. Chemical industries such as Caustic soda and Soda ash plants use salt as the basic raw material. Salt is the backbone of chemical industries and number of downstream chemicals are manufactured from salt. Seawater is the major source of salt and most of these chemical industries make their own salt using solar evaporation of seawater using traditional methods with salt pans. Large area of land is required for this purpose and solar evaporation is a slow process and it takes months together to convert seawater into salt. It is also labor intensive under harsh conditions. The author of this article has developed an innovative technology to generate fresh water as well as salt brine suitable for Caustic soda and Soda ash production. By using this novel process, one is able to recover almost 70% fresh water against only 40% fresh water recovered using conventional SWRO process, and also recover about 7- 9% saturated brine simultaneously. Chemical industries currently producing salt using solar evaporation are unable to meet their demand or expand their production due to lack of salt. The price of salt is steadily increasing due to supply demand gap and also due to uncertainties in weather pattern due to global warming. This result in increased cost of production and many small and medium producers of these chemicals are unable to compete with large industries. Moreover, countries like Australia who have vast arid land can produce large quantities of salt with mechanized process competitively; Australia is currently exporting salt to countries like Japan, while countries like India and China are unable to compete in the international market with their age old salt pans using manual labor. In solar evaporation the water is simply evaporated. Currently these chemical industries use the solar salt which contains a number of impurities, and it requires an elaborate purification process. Moreover the salt can be used as a raw material only in the form of saturated brine without any impurities. Any impurity is detrimental to the Electrolytic process where the salt brine is converted into Caustic soda and Soda ash. Chemical industries use deionized water to dissolve solar salt to make saturated brine and then purify them using number of chemicals before it can be used as a raw material for the production of Caustic soda or Soda ash. The cost of such purified brine is many times costlier than the raw salt. This in turn increase the cost of chemicals produced. In this new process, seawater is pumped into the system where it is separated into 70% fresh water meeting WHO specifications for drinking purpose, and 7-10% saturated pure brine suitable for production of caustic soda and Soda ash. These chemical industries also use large quantities of process water for various purposes and they can use the above 70% water in their process. Only 15-20% of unutilized seawater is discharged back into the sea in this process, compared to 65% toxic discharge from convention desalination plants. This new technology is efficient and environmentally friendly and generates value added brine as a by-product. It is a win situation for the industries and the environment. The technology has been recently patented and is available for licensing on a non-exclusive or exclusive basis. The advantage of this technology is any Caustic soda or Soda ash plant located near the seashore can produce their salt brine directly from seawater without stock piling solar salt for months together or transporting over a long distance or importing from overseas. Government and industries can join together to set up such plants where Governments can buy water for distribution and industries can use salt brine as raw material for their chemical production. Setting up a desalination plants only for supplying drinking water to the public is not a smart way to reduce the cost of drinking water. For example, the Victorian Government in Australia has set up a large desalination plant to supply drinking water. This plant was set up by a foreign company on BOOT (build, own and operate basis) and water is sold to the Government on ‘take or pay’ basis. Currently the water storage level at catchment area is nearly 80% of its capacity and the Government is unlikely to use desalinated water for some years to come. However, the Government is legally bound by a contract to buy water or pay the contracted value, even if Government does not require water. Such contracts can be avoided in the future by Governments by joining with industries who require salt brine 24x7 throughout the year, thus mitigating the risk involved by expensive legal contracts.

Monday, June 11, 2012

Innovative desalting technolgy for Chemical industries


Sodium chloride commonly known as ‘ common salt ‘ is a basic raw material for the production of a wide range of chemicals including Caustic soda and Soda ash. The cost of salt has been recently increasing steadily due to wide demand and supply gap all over the world. This in turn has increased the cost of all other chemicals derived from salt and this situation is expected to continue in future. Salt industry has been traditionally using a ‘solar evaporation’, an age old technique from antiquity. The technology involves pumping of seawater on large area of arid land and allowed to evaporate as the concentration of salt increases. The brine then passes on through the various ponds, with the sodium chloride content rising from 2% to 25%. This increasing salinity gives the ponds a distinctive pink color, as algae in strongly saline solutions produce a red pigment called haematochrome. The Red Sea is red for the same reason. The saturated brine is pumped to smaller ponds where nature continues its work of evaporation. Once the volume has been reduced to 10.2% of the original, any further concentration results in the deposition of sodium chloride. From September to February more brine is added until at least 25 mm of salt has settled and it is time for harvesting. The brine remaining (called "bitterns") is a saturated solution of NaCl, with the other salts present at concentrations well below saturation. This is pumped out to sea just before the harvest is gathered, as these ions would contaminate the salt if all the water were evaporated off. For four to six weeks beginning in early March, mechanical harvesters scoop up the crystallized salt and load it on to trucks that shuttle back and forth across the ponds to the washer. In the two washing plants the salt is washed in clean saturated brine, in which the other salts, present as impurities, dissolve. From there hundreds of tones of clean washed salt are discharged daily on to the stacks for storage - up to 10,000 tons per day. During winter no more salt is recovered, but the plant continues its regular work of processing and beggaring the stockpiled salt. But this raw salt has number of impurities such as Calcium, Magnesium and Sulfate ions which are harmful for the production of further chemicals. Though the cost of producing salt is cheaper by solar evaporation, the cost of purifying salt from above impurities and making suitable brine for chemical production is expensive .The cost of salt used in chemical processing industries after transportation and purification increase to whopping $ 200 and above. Many Asian countries such as Japan, South Korea, China, Taiwan and Indonesia are major importers of salt. The salt import by the above importers in Asia pacific region between 2000 and 2009 has increased by 6 million tonnes, equal to 40% or 4.6% per annum.In four years between 2005 and 2009, the price of salt increased by US$25/Mt, equal to 83% or 16% per annum.The average price of imported salt varies between US$40 to $47/Mt. (Ref: Salt partners). Erratic weather patterns, sea level rise, Tsunami, inundation, flooding and unseasonal rains have hampered salt production all over the world. The chemical industries are facing an uncertain future and unpredictable pricing of salt. Prolonged winter in Europe and US and other parts of the world have pushed the demand for salt for de-icing. India is the third largest and cheapest producer of salt in the world with lowest labor cost. But even in India, the prices of salt have gone up recently from Rs.600 to Rs.1000/Mt. An Australian company has developed and patented an innovative technology to solve the above problems. The company uses membrane technology to produce Sodium chloride brine directly from seawater suitable for all chemical products in the downstream. This novel technology separates seawater into salt and drinking water, after all seawater contains about 95% pure water. It can solve the problems of many mining companies in Australia who need Caustic soda as well as water for their processing.

Saturday, May 19, 2012

Sun,sea and chemical industries


How many of us think about the Sun and Sea, when you drink ‘Mineral water’ from that ‘PVC bottle’; or think about the PVC cables that transmit power to your home; or eat meal with a pinch of salt or bicarbonate; or when your municipal water treatment plant use Chlorine to disinfect your drinking water? All these come from sea water energized by sun’s light, day after day, for several decades. Every year 111 billion liters of seawater are evaporated using solar energy to produce 1.1 billion liters of brine. The amount of solar energy required to produce this, is equal to 11 million tons of coal, valued at US$ 1.10 billion. The brine is then crystallized to produce 2 million tones of solar salt, the essential raw material for 18 basic inorganic chemicals, including soda ash. Soda ash and Caustic soda are two fundamentals raw materials to chemical industries, as steel is to the engineering industries. This above statistics applies to one single manufacturer, and there are hundreds of manufacturers around the world. Sun and sea are two great gifts of Nature to mankind. But industries use three great resources namely Sun, seawater and a vast stretch of land often free of cost. Companies convert seawater into salt using sun’s energy, manufacture valuable chemicals, sell them with profits and then dump all toxic wastes on the soil and discharge all the industrial effluents back into the sea, polluting not only the source of their raw materials but also killing thousands of marine species they call ‘sea’ as their home. Governments and EPA (government agencies) turn a blind eye to such pollution and give them clearance year after after year in each country for several decades, because they depend on taxpayer’s money to run their Governments. The manufacturer utilize these natural resources free of cost or at a fraction of a cost and make huge profits to their shareholders and pay tax to the Government, to make sure that Governments don’t interfere with their activities. What is really happening is few rich and powerful are able to exploit the natural resources and enrich themselves with the help of Governments at the cost of earth, water and air, we human beings habitat. This avaricious exploitation of Nature has driven not only human beings but many animals and species to extinction. Basic needs of life such as water and air are polluted, man-made waste are dumped indiscriminately on soil, polluting the earth and ground water. The plastic manufactured using Nature’s sun and sea water, are dumped back on earth as non-biodegradable pollutants. This is how we repay Nature. Human beings have caused an irreversible damage to Nature in the name of science, technology and industrialization at the cost of future generation, while enriching few rich and powerful. The damage is irreversible, because we are forced to continue the same path in order to avert any disruption to our growth story. As long as we value materials over morals and ethics, there is no future and Nature will eventually turn its back with vengeance. We value how much a person is worth financially rather than, what a person can contribute to uplifting human beings and Nature. This is the crux of all problems in the world, including the financial crisis we are currently facing. We created the monster called ‘materialism’ and the same monster is now destroying humanity.