Deep Dive: The Inertial Evaporator and its Open Oscillatory Approach

System Implementation

Liquid piston inertial evaporator systems will within couple of decades be installed in series at most industrial sites globally where they will efficiently upgrade otherwise lost low-grade thermal energy into valuable process steam.
To the right, an indicative implementation diagram showing three units arranged in series. The waste heat is removed in steps incrementally and then returned. Several units eject into the same steam header helping to reduce potential pressure fluctuations. Potential superheat in the ejected steam is quickly reduced to saturation pressure in the steam header. The steam header can be connected directly to existing steam systems or (as shown) to a heat exchanger. The condensate is then returned back to the inertial evaporator systems to maintain constant water levels.

Papers & Presentations

Industrial Waste Heat — Brief Summary

One third of the world's energy is used by industry to manufacture everything we take for granted in our modern world. For example fertilizer, paper, foodstuffs, textiles, plastics, rubbers, all oil products, steel, cement etc. etc.

To improve energy efficiency, lower costs, and reduce emissions, most industrials implement ways to recover and reuse otherwise wasted thermal energy. The most common approach leverages solutions like cleverly arranged heat exchangers that transfer heat directly from hot process streams that need cooling (such as exhaust gases and cooling water) to streams that require heating. In many cases, excess heat is furthermore collected and exported to a nearby district heating network, greenhouses, or an adjacent industrial process.

Despite these efforts, a substantial portion (20-50% depending on sector/process) of the energy is discarded as ultra-low-grade waste heat (lower than ~60°C). This low-temperature heat is difficult to reuse because most industrial processes require steam or higher-grade heat (130-170°C or above). As a result, many plants are forced to shed this thermal energy to the atmosphere via radiators or simply pour it down the drain as warm cooling water.

Current Alternative Systems

An established category of solutions for upgrading such low-grade waste heat into process steam is the integration of Large Heat Pumps (LHP) with Mechanical Vapor Recompression (MVR), typically via so called flash tanks. These combined "LHP + MVR" system packages are offered by established OEMs and technology providers, including Howden, Turboden (a Mitsubishi Heavy Industries group company), GIG Karasek, Piller Blowers & Compressors, Atlas Copco, and others.

A typical LHP + MVR system consists of three steps:

1. A closed-cycle large heat pump first upgrades the available low-grade waste heat. It does so by concurrently cooling a ~40°C waste-heat source, thus extracting its thermal energy which it uses to heat up thermal fluid to a higher intermediate temperature level, 70-90°C, or more in the case of high-temperature heat pumps (HTHPs). It's similar to how refrigerators work, cooling the food inside by moving the "inside-heat" energy to the hot coils that used to be visible on the backside of refrigerators.
2. The intermediate heat from the thermal fluid is transferred to an evaporator vessel (often referred to as a vacuum flash tank). The tank is operated at sub-atmospheric pressure which reduces the boiling point of the water in it. Due to the reduced pressure the 80°C thermal fluid from the heat pump is sufficiently hot to boil the water in the evaporator vessel and generate low-pressure steam or vapor from the water (or process condensate).
3. One or more MVR compressors then extract and compress the low-pressure vapor. The rapid and powerful compression simultaneously increases the steam's pressure and temperature, quickly turning it into useful saturated steam suitable for direct process use, typically in the range of 130-170°C or higher, depending on the number of compression stages and system design. Because steam becomes superheated when it is "squished" the process is typically in several stages allowing for the repeated removal of its superheat (it's not really the temperature but the extra pressure of superheated steam no one really cares for).

The LHP + MVR approach enables process steam generation from waste heat supplementing steam already generated by existing plant boilers. Generating process steam this way can be far more cost-effective than producing the same amount in on-site gas boilers. An important caveat is the fact that electrical energy is typically 3-5x more expensive (per Joule) than natural gas. Because of this unfortunate price discrepancy, the efficiency (COP) of electrically driven waste-heat upgrading equipment is of paramount importance.

The design and specifics of LHP + MVR systems and high-temperature heat pumps vary between manufacturers, and size ranges from a couple of kWth to several MWth. The technology is now considered mature and has been successfully integrated in thermally intensive industries such as pulp & paper, food/beverages and chemicals.

Other technical solutions are less mature or have attributes making them less comparable to Hydram's solution (such as ORCs, AHTs, THTs, TVRs, thermoelectrics and others).

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