Converting waste heat and wastewater into concentrated residue: Lt Col Satish M Vaidya

Just as nature leaves no waste, we should recycle everything to reduce the pressure on resources and stop environmental degradation. A proposed Heat-Siphon* (a modified heat pipe with an inverted ‘U’) carries out low-temperature distillation at a small temperature difference (∆T) using low-grade waste heat to produce concentrated residue and pure distillate (value-added by-products) and can meet our ever-increasing-demand of food, water, and energy.

Incubees: What is the heat-pipe concept?

Lt Col Satish M Vaidya: Heat-pipe is a sealed hollow metal tube containing a relatively small quantity of working fluid (coolant) with the remainder of the pipe being filled with the vapour phase of the liquid, all other gases being evacuated. It transfers the latent heat of evaporation irrespective of ∆T, cross-section area, distance, or time. Heat pipes (using ammonia) keep permafrost frozen at minus 6° C temperature and maintain the ground’s load-bearing capacity.

Incubees: What is the concept of ‘Low-Temperature Distillation’ and the technique used?

Lt Col Satish M Vaidya: The ‘Low-Temperature Distillation’ concept was initially based on solar-still (survival technique that replicates the water cycle over a day/night cycle) and has evolved into vacuum-aided distillation with the following natural phenomena: –

• Condensation inside discarded PET water bottles over a day/night cycle and outside glass windows of AC rooms (5°C cooler) during monsoons.
• The boiling point of water drops by 3.5°C and the temperature drops by 6.5°C for every 1000 m increase in altitude.

Incubees: What inspired you to work on this theory and have you proven the concept?

Lt Col Satish M Vaidya: I have been working on this concept for over 21 years and have proved the concept with a model having two glass flasks and a vacuum pump. At ∆T of 20°C, it achieved rapid distillation with reduced internal pressure (Evaporator at 50°C and condenser at 30°C). On the other hand, there was no distillation with a normal internal pressure at ∆T of 65°C (Evaporator at 95°C and condenser at 30°C). It needs minimal energy and can be called Heat-Siphon*.

Incubees: What applications do you visualise for Heat-Siphon*?

Heat-Siphon* converts waste heat and wastewater into concentrated residue and pure distillate; turning two liabilities into two assets. Value-added by-products are possible in many applications; with 10-liter versions (for food processing) to 2000 liters (for desalination/ wastewater recycling/ sugar-making). Some applications visualised are as follows: –

• Heat-Sink. Machines use energy sources (causing global warming) and heat sinks (using even more energy to force out waste heat). Cooling towers (consuming about 1000 kWh of electricity each daily) remove waste heat from compressors, power plants, etc; increasing relative humidity (heat index). Heat-Siphon* needs barely 5% of this electricity to drain out low-grade waste heat (this efficient heat sink saves considerable energy) and also produces distilled water. India consumes 1386 Tera Wh of electricity daily (70% is from coal) and a 25% reduction in electricity consumption corresponds to 47.8 billion tons of coal annually.

• Desalination/ Salt-making. Reverse-Osmosis (RO) plants need infrastructure, power, and recurring expenditure. Heat-Siphon* would produce distilled water and brine/ salt.

• Effluent Treatment. 80% of wastewater (of which 22% is highly polluting industrial effluent) is released untreated due to the high operating cost of ETPs. Heat-Siphon* can convert effluent into distilled water and concentrated residue (for recovery of chemicals, etc.); to resolve both water supply and sewage disposal.

• Food Processing. Concentrating/ desiccating surplus perishable fruits/ vegetables and purees increases their shelf life to avoid wastage. Sugarcane juice, fruit juices, milk, eggs, etc. are degraded at high temperatures and can be concentrated/ dehydrated at low temperatures by Heat-Siphon* as follows: –
  • Sugarcane Juice. Sugarcane juice is concentrated in closed vacuum pans, where vacuum pumps (125-250 HP) lower its boiling point to prevent caramelisation/ discoloration.
  • Milk, Fruit Juices, and Coconut Milk/ Tender Coconut Water become compact and longer lasting when condensed.
  • Eggs coagulate at high temperatures and can be desiccated with Heat-Siphon*.
  • Distilled water. The global market for bottled water is worth USD 342.4 Billion in 2023. Distilled water with added minerals is ideal for drinking and local production eliminates transportation/ packaging. It is also ideal for boilers, washing semiconductor chips, etc.
  • Crystallisation of salts and Fractional Distillation of alcohol, vinegar, oils, solvents, etc. will be efficient.

Incubees: What are the advantages of Heat-Siphon?

Lt Col Satish M Vaidya: Heat-Siphon* can work in extremely cold climates (unlike cooling towers, where coolant water freezes). It reduces pressure on traditional water sources. Zero discharge of effluent eliminates water pollution. It can use wastewater (also contaminated with arsenic/ fluoride) and brackish/seawater. It can use abundant solar and low-grade waste heat. Cold storage and sugar mills can be synergetic. Energy saved is energy produced. It would prevent deforestation and facilitate reforestation to sequester carbon dioxide.

Heat-Siphon* is compact and efficient as compared to RO Plant, seawater greenhouse, atmospheric water generator, and GALMOBILE.

Incubees: Why are you passionate about the Heat-Siphon*?

Lt Col Satish M Vaidya: I am convinced that Heat-Siphon* is highly feasible, as complex technology exists for helium release valves in Rolex divers’ watches and submarines going deep underwater. Since it is entirely new, users may resist change from existing technology. However, prototypes can be designed for the steady, uninterrupted, and automatic operation of various applications.

Thomas Newcomen invented the first fuel-burning atmospheric engine in 1712, which James Watt used in 1776 to make the steam engine. It started the Industrial Revolution that can be sustainable with Heat-Siphon*. Expenditure is quantifiable, but savings from averted environmental disasters, emergencies, breakdowns, etc, are not. Reducing fossil fuels/ carbon emissions conserves the environment, creates wealth, eliminates presently inevitable costs, and makes life sustainable. Its potential benefits cannot be quantified; like the value of a head load of water carried by women in water-deficient areas.

We are used to shortages and scrounging for natural resources, which degrades the environment. Recycling wastes creates abundance and also stops degradation. The question is not whether we can afford the change, but whether we can afford not to change. Although the concept is simple, it requires precise combinations of variables. I applied for a patent in 2010, but am ready to offer it freely to all willing pioneers. I visualise many problems and want to ensure their success. I am open to contradictions/ anomalies in the above.