Article Index

Environmental Friendly Cooling and Heating

by using the Innovative Zeolite/Water Adsorption Technology

Zeo-Tech has developed a new energy conversion process for the efficient generation and storage of heat and/or cooling power. Driven by a heat source, this process is solely based on the material zeolite and water and is therefore fully compatible with the most stringent environmental regulations. Up to 160% efficient.

Dr Peter Maier-Laxhuber & Zeolite Cooler

Fundamentals of the Zeolite/Water Adsorption Technology

The natural mineral Zeolite has the property to attract (adsorb) water vapor and to incorporate it in its internal crystal lattice while releasing heat at the same time.

If this process proceeds in an evacuated (airless) environment the attraction of water by the zeolite is so forceful that the internal pressure drops dramatically. The remaining water in an attached vessel evaporates, cools down and freezes immediately due to the heat of evaporation. The resulting ice can be used for cooling and air conditioning while the simultaneously produced heat of adsorption within the zeolite tank can be utilized for heating. If a valve is included between the two vessels, the heat or cold production can be interrupted for any periods without loss of energy.

The first phase of this process proceeds up to the point when the zeolite is saturated with water. The reverse process is initiated by heating the zeolite at high temperatures in the second phase. The adsorbed water molecules are forced to evaporate (desorption). Condensation takes place in the water tank (condensor). The sequence of adsorption/desorption processes is completely reversible and can be repeated indefinitely.

 

 

A nearly continuous cooling power is accomplished if two or more of these sorption devices are operated in a phase-shifted manner. The regeneration can be performed with electric energy or – preferably from the perspective of primary energy usage – with heat from combustion processes or even with solar collectors.

As shown in the figure, the driving energy source is heat (100 %) which picks up an additional 30 % of net cooling power and thus provides a usable net heating power of 130 % as the overall result of the conversion cycle. If this system is applied in dual use mode for heating as well as cooling in parallel, the overall net effect amounts to 160 % of the expended heat input (100 %), provided as heat output (130 %) and cooling power (30 %).

Even with electrical heating, a sorption system provides considerable energy savings and a corresponding reduction of carbon dioxide production.
With other input heat sources the energy saving potential is much higher, with corresponding environmental benefits. Even the single use mode, utilizing only heating or only cooling power, is comparable or better (with respect to energy utilization) than any conventional technology.

Zeolite

The name zeolite is a general term for a stonelike material which consist of crystalline metal-alumo-silicates with a large internal surface area of up to 1000 m²/g, strong electrostatic fields in the crystal lattice and with a volumetric density of about 0.8 kg/dm³. The word zeolite is of greek origin and means – directly translated – »boiling rock« which describes the effect which is to be seen if water is poured over dry zeolite. In 1925 the process of water and methanol separation using zeolites was observed for the first time. And due to this separation action (sieve action) the name "molecular sieve" was later attributed to zeolites.

Zeolites are non-poisonous, inflammable, are naturally available in abundance and are therefore compatible with the environment. More than 40 natural and 100 synthetic zeolites are known.

The most important property of a number of zeolites is their ability for reversible adsorption of water. Even after several thousand adsorption/desorption cycles the structural changes of the crystal latice are insignificant if the process parameters pressure and temperature do not exceed certain limits. – The application diversity of zeolites is tremendous: they are applied as molecular sieves, as adsorbents, as catalyst in cracking of hydrocarbons in the pretro-chemical industry, as filler component in paper production and as ion exchange material in detergents

Currently the chemical industry produces more than 1.4 million tons of synthetic zeolite annually and it can be expected that the world wide demand and consequently the production will further increase. The price, e.g. for laundry detergent zeolite is between 1.00 and 8.00 DM/kg, depending on the type and consistency of material delivered. The price for specialized zeolites is higher.

The basic building blocks of zeolites are tetrahedras consisting of four oxygen anions and one centrally positioned silicon or aluminum cation.Zeolites are classified according to the various tetrahedral frameworks formed by these basic building blocks. The structure of the synthetic zeolites of types A, X and Y which have gained importance in industrial processes, are shown in the figure. The aluminum and silicon atoms are positioned at the junctions while the oxygen atoms form the bridges between the tetrahedras. The difference in electro-chemical charges between the aluminum and silicon atoms per one aluminum atom results in a non-compensated negative charge. The balance is restored by metal cations which occupy preferred positions. Because of the strong local electrical dipole moment in the lattice framework, zeolites adsorb all polar and non-polar molecules that will fit into their specific framework. This adsorption process is accompanied by release of heat, the »heat of adsorption«. Theoretical and experimental studies have determined quantitative heat of adsorption values for zeolite based thermal processes.


Ice-Quick Demonstrator

The Ice-Quick is a small device to demonstrate the adsorption technology with the sorption pair water/zeolite. It consists of a zeolite filled cartridge, connected via an adaptor to a plastic cup, which contains some water, and which is evacuated by means of a hand-vacuum pump.

After approx. 10…20 strokes with the hand-vacuum pump the inside pressure is reduced below the vapour pressure of the water at ambient temperature, and the water start to boil. Air gases go out of the water and starts to bubble on the bottom of the glass. (The more air is removed out of the system, the better the adsorption of water vapour. The vapour above the water surface is adsorbed in the cristalline structure of the zeolite. As a result, the remaining liquid water cools down.) After a few more strokes the water calms down and finally begins to freeze. After some time the water is completely frozen: 50 g of water at a temperature of 10 °C can be cooled down and frozen within 30 sec with 500 g of zeolite. The average specific cooling power results to 390 W/kgZeo.

This process can be repeated 8…10 times with arbitrary intervals until the zeolite is saturated. The zeolite has always to be cooled down to the ambient in between processes for the adsorption to function properly. For desorption (regeneration) the zeolite has to be heated up to 250 °C for a short time. When the zeolite is cooled down again to 20 °C it is ready for further ice production.


Solar Powered Refrigerator

Developing countries have a great need for cooling of food and medical supplies. Refrigerators are very expensive and require a electric power source. While reliable electric power supply is only available in the industrialized centers of developing countries, solar power is available and – especially in the southern areas – is reliable. Up to now, solar power has not been used for cooling.

Zeolite/water sorption systems can now provide a reliable and economic solution for these cooling needs.

The equipment consists of a refrigerator (in this case a 55 liter box-shaped cooler), powered by solar energy, with a built-in evaporator, one or more zeolite containers and a parabolic, concentrating solar collector, developed by E.G. Solar.

The cooling system is designed such that it can be produced locally without need for expensive electrical tools; maintenance and repair can be performed locally due to the simple design.

The investment for the cooling device is much lower than a solar driven compressor system of the same size which is powered by electric solar cells (costs about DM 3,000.--)

The solar collector can also be used for cooking.


Standard-Cooling

The Standard-Colling system is used – as described above – for the trolleys, for beverage dispensers and for food refrigerators. It consists of two adsorbers, one condenser and one evaporator (and some addi- tional compenents which are not shown in the right figure).

The two adsorbers with 8 kg zeolite granulate each operate in alternating fashion. Via heat exchanger loops the heat available after desorption and also the heat produced during adsorption is removed. Adsorber and evaporator are coupled by one-way valves which are opened or closed depending on the pressure in the two vessels. The desorbed water vapour flows to the condenser and (after condensation) through a capillary pipe (which also contributes to the heat removal) back to the evaporator. The water charge in the eva- porator is about 5 ltrs. For optimisation of the evaporation the surface area in the evaporator is enlarged considerably by constructive means. The »cooling power« is transferred by a heat transfer medium pumped in a closed cycle through flexible hoses between evaporator and the cabinet to be refrigerated, where the cooling effect is achieved through a heat exchanger.

Monitoring and control of the system are performed by a programmable electronic controller. For a heating power of 6.6 kW maximum the cooling power of this system, which is available as protoype, amounts to about 2.8 kW. This covers a cooling temperature range of down to 0 °C.


Zeolite Heat Pump with Integrated Ice-Storage

Characteristics of the zeolite heatpump with integrated ice-storage:

Significant energy savings – referring to the state of the art technologies (e.g. condensing boiler): approx. 25 % ; at hot water temperatures of 60 to 70 ºC

Approx. 75 % less heat from the ambient needed compared to an electrical heat pump

Ambient heat can easily be provided, for example with CPC collectors also in the autumn and in the winter ; possible ambient heat sources are: heat recovery systems

Flue gas can be cooled down below 0 ºC, therefore a significant cleaning of the flue gas due to condensation of harmful substances is more easily possible than with conventional condensing boilers

Add-on capability: gas-fired air-conditioner; supply of considerable electrical power for the functioning of the air-conditioner is not needed

Zeolite heatpump with integrated ice-storage is very easy to maintain and a long system lifetime

Cost savings due to the use of small ambient heat exchangers

Zeo-Tech GmbH is going to build and optimise a zeolite heatpump with integrated ice-storage for a typical one-family house with a rated heating power of approx. 10 kW.

 

 

Peter MAIER-LAXHUBER, et al.: Zeolite/water adsorbtion heating/cooling, yields up to 160% heat/cold;

articles & 26 patents


Peter MAIER-LAXHUBER, et al.

Zeolite/Water Adsorption Cooling/Heating

http://www.zeo-tech.de/e_index.htm

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