LiBr Vapor Absorption Machine (LiBr VAM)

Field of invention

This invention relates to a LiBr Vapor Absorption Machine (LiBr VAM).

Background

The heat sources for a LiBr VAM are mostly one of the following:

1. Live steam at around 8 kg/cm, sup. 2 generated from any steam boiler.

2. Pressurized hot water generated from any hot water generator and normally pumped through the generator of a VAM.

3. Direct firing of liquid / gaseous fuels in a High Temperature Generator (HTG).

4. Use of Exhaust gases from DG sets / micro turbines and the like, for recovering its waste heat directly in a HTG.

5. High temperature thermic fluid pumped through the tubes of a generator.

6. Waste heat in any form such as low pressure steam / hot water / Flue gases etc.

Thus main drawbacks for the existing LiBr VAM are the requirement of additional equipment for overall system and associated higher capital cost. Another limitation is that in case of a hot water generator, a pump is required to force working medium through the generator tubes or in case of a boiler for forcing the condensate back to the boiler. There is high operating cost associated with it. In the case of a steam boilers, the system is an open loop type and the total hold up of such a boiler generally exceeds 22.75 liters, bringing it under the purview of IBR.

Less availability due to annual inspection and mechanical maintenance in case of steam boilers. The limitation of direct firing of liquid / gaseous fuels in LiBr VAM is that the cost of such fuels is comparatively high and it is not always commercially viable to fire such fuels to produce cooling effect through a VAM.The availability of waste heat or exhaust gases from a DG sets and the like is limited and strictly applicable on case to case basis and is viable only when the DG set is running on base load continuous.

Over the years there is steep increase in electricity and oil prices. There is also need for environment friendly, green technologies which reduce the operating cost as well as emissions especially CO2. Solid fuel fired vapor absorption machines working on biomass provide unique combination of environment friendly absorption technology which uses natural refrigerant and use of biomass which not only substantially reduces operating cost but also reduces CO ₂ emissions.

Existing Knowledge

US6405551 discloses an apparatus having a refrigeration cycle includes a compressor, a condenser and an evaporator. The heating apparatus has a first heat exchanger and a second heat exchanger, where the first heat exchanger is selected as a heat source, and the second heat exchanger is selected as either a cooling or heating source. The first heat exchanger and the second heat exchanger are connected in series with each other in a refrigerant circuit. A heating medium is circulated in a heat transfer device which is connected to the first heat exchanger. Bathwater of a bathtub and water of a hot-water storage tank are heated through the heat transfer device indirectly by the first heat exchanger.

US2002026803 discloses apparatus for controlling a refrigeration cycle for circulating a refrigerant through a compressor, a heat exchanger for condensation, a flow rate control valve, and a heat exchanger for evaporation, connected each other which comprises of a first operation means for changing a heat exchanging capability of said heat exchanger for condensation, a second operation means for changing a heat exchanging capability of said heat exchanger for evaporation, a means for operating a running capacity for changing a running capacity of said compressor, and a control means for reducing a difference between a running condition on a high pressure side or a low pressure side of the refrigeration _. cycle and a target, wherein when a difference between a running condition on a high or low pressure side and its target is reduced, the control means bring the running condition closer to the target, minimizes a consumption energy, and bring a temperature difference of a heat exchanging fluid between an inlet and an outlet of the heat exchanger for condensation closer to a target temperature difference.

US2004112073 discloses refrigeration cycle for a vehicle air conditioning system allows the refrigerant-to-refrigerant heat exchanger to exchange heat between a high-pressure liquid refrigerant, which is delivered from the sub-cooling condenser and directed to the evaporator, and a low- pressure refrigerant having a liquid and gas phase, which is delivered from the evaporator and directed to the compressor. The refrigeration cycle also allows the amount of the refrigerant circulating through the refrigeration cycle to be adjusted in response to the level of sub-cooling upstream of a throttle hole of a reverse sub-cooling control valve to thereby indirectly control the level of superheating on the outlet side of the evaporator.

US2004216483 discloses a vapor-compression refrigerant cycle system with a refrigeration cycle and a Rankine cycle includes a compressor, a radiator, a gas-liquid separator, a decompression device and an evaporator. In the vapor-compression refrigerant cycle system, a liquid pump is disposed for supplying the liquid refrigerant in the gas-liquid separator to a heater for heating the refrigerant, a cooling means is provided for cooling the liquid refrigerant to be sucked into the liquid pump, and an energy recovery unit for expanding the refrigerant flowing out of the heater is disposed to recover thermal energy in the refrigerant from the heater. When the Rankine cycle is set so that the energy recovery unit recovers the thermal energy, the cooling means cools the liquid refrigerant to be sucked into the liquid pump.

Objects of the invention

One of the objects of the present invention is to provide an apparatus which has a lower operating cost.

Another objective of the present invention is to provide an apparatus wherein the heat is recovered from combustion of solid fuels.

Yet another objective of the present invention is to provide an apparatus which utilizes solid fuels directly as a heat source for providing refrigeration effect.

Yet another objective of the present invention is to provide an apparatus wherein crystallization of the LiBr solution is prevented.

Yet another objective of the present invention is to provide an apparatus which is robust.

Yet another objective of the present invention is to provide an apparatus which is easy to manufacture.

Summary of the Invention:

In accordance with the invention there is provided an apparatus for providing refrigeration effect comprising an LiBr vapor absorption machine having an absorber, an evaporator, a condenser, a low temperature generator , a low temperature heat exchanger, a high temperature heat exchanger , a refrigerant heat exchanger , an LiBr solution pump and a refrigerant pump; the cold refrigerant being provided from the evaporator characterized in that the high temperature generator of the machine is separated out of the machine and the said generator has a furnace which is directly fired using solid fuel.

Typically, the high temperature generator includes a first heat exchanger adapted to receive weak LiBr solution from the absorber and is adapted to generate refrigerant vapor and supply the refrigerant vapor to the low temperature generator and also to form concentrated LiBr solution and supply the concentrated LiBr solution to the high temperature heat exchanger.

Typically, the high temperature generator is of tube and shell construction, the tube section of the generator being adapted to receive the flue gases from the furnace and the shell is adapted to receive weak LiBr solution from the absorber.

Alternatively , the high temperature generator is of tube and shell construction, the tube section of the generator being adapted to receive the weak LiBr solution from the absorber and the shell is adapted to receive flue gases from the furnace.

Typically, a dump condenser is provided on line between the first heat exchanger and the low temperature generator of the vapor absorption machine.

Typically, the dump condenser is of the tube and shell type, the tube portion adapted to receive cooling water and the shell portion adapted to receive refrigerant vapor from the first heat exchanger and store condensed refrigerant inside the shell.

A valve means is provided to divert refrigerant accumulated in the dump condenser to the high temperature generator to reduce the concentration of the LiBr solution in the first heat exchanger.

In accordance with one embodiment of the invention the valve means includes a solenoid valve and an isolation valve combination.

Typically, the solenoid valve is of the normally closed type.

Typically, the first heat exchanger is in the form of at least one array of tubes arranged within the shell.

Typically, the furnace has an approximately semi hemispherical configuration.

Typically, the first heat exchanger has a plurality of arrays of tubes arranged within the shell surrounding the furnace.

Typically, the dump condenser shell has an outlet connected above the liquid level in the first heat exchanger.

Typically, the tube section has a header unit and the dump condenser shell outlet is connected to the header.

Typically, a dust separation and collection means connected to the furnace.

Brief Description of the Drawings

Figure. 1 represents a process diagram for solid fuel combustion system along with a high temperature generator and essential components of vapor absorption machine in accordance with the present invention;

Figure.2 represents the cross sectional view of the heat transfer generator (HTG) along the section XX as shown in Figure 1;

Figure. 3 represents the alternative design for heat exchanger tubes of the HTG as shown in Figure 1 ; and

Figure. 4 represents yet another alternative design for the heat exchanger tubes of the HTG as shown in Figure 1.

Detail description of the invention with reference to the accompanying drawings:

Figure 1: Shows the new design of a high temperature generator (HTG) (29) wherein, consists of a fuel firing mechanism (6), a combustion air supply system (5), heat exchanger tubes (9) to transfer heat from exhaust gases to the LiBr solution on the outer side of tubes. It also has a LiBr weak solution inlet connection, Intermediate solution outlet connection, set of eliminators and vapor outlet connection.

Figure 1 also shows essential components of an LiBr VAM comprising major components such as a Lower shell (11) comprising an evaporator (12) and an absorber (13), an upper shell (14) consisting of a condenser (15) and a low temperature generator (LTG) (16), Set of heat exchangers

such as a low temperature heat exchanger (17), a high temperature heat exchanger (18) and a refrigerant heat exchanger (19), a LiBr solution pump (20) and a refrigerant pump (21). Major protection and safety devices consisting of a dump cooler (22). The dump condenser (22) has a cooling tube (23) through which cooling water flows. Other components are a shell (24), a vapor inlet pipe (25), a refrigerant liquid outlet pipe (26), a solenoid valve (27) and an isolating valve (28).

Figure 2: Shows a solid fuel combustion system and its accessories comprising; solid fuel storage and conveying system (1), a Combustion air fan (2), a combustion chamber (8) for carrying products of combustion product i.e. exhaust gases out of the furnace, heat exchanger tubes (9) to transfer heat from exhaust gases to the LiBr solution on the outer side of tubes and exhaust gas chamber (10) to collect cooled exhaust gases from the tubes, a dust separation and collection equipment (3), an induced draft fan (4), a Combustion air supply and distribution system (5) and a fuel firing mechanism (6).

Figure 3: Shows one of the embodiments of the invention wherein direct solid fuel fired HTG heat exchanger tubes are connected to LiBr VAM. The HTG and furnace is having a circular cross section (30).

Figure 4: Shows another embodiment of an invention where the solid fuel fired HTG heat exchanger tubes are connected to LiBr VAM. The HTG and furnace have a rectangular cross section (31).

Detail description of vapor absorption cycle in accordance with the present invention:

Accordingly, in this system different types of solid fuels (coal, biomass, lignite etc) are burnt in the furnace part of new HTG. The products of combustion pass through the heat transfer tubes of HTG. The heat from the flue gases is transferred to the LiBr solution which is on the outer side of heat transfer tubes as shown in figure 2.

In the present invention water is used as a refrigerant and LiBr solution as an absorbent. The absorber and the evaporator are located in the same shell. The refrigerant water is circulated and sprayed over the evaporator tubes in the evaporator (12) where it is converted into water vapor. These water vapor formed absorbs heat from the chilled water (CHW) which passes through the evaporator tubes and hence cools the same further the refrigerant water vapor enters the absorber (13) and is absorbed by LiBr solution sprayed over the absorber tubes. The heat of absorption is taken away by cooling water (CW) flowing through the absorber tubes. The strong LiBr solution gets weaker in LiBr after absorbing water vapor. The weak solution of LiBr thus formed in the bottom of the absorber is pumped to the high temperature generator (29) by the weak solution pump (20) through the low temperature heat exchanger (17) and the high temperature heat exchanger (18). In the high temperature generator LiBr solution is heated and gets concentrated. The refrigerant water vapor thus formed is sent to tube side of the low temperature generator (16) where the water vapor condenses. The concentrated solution from high temperature generator is sent to the shell side of the low temperature generator (16) where it is further concentrated to form strong solution. The water vapor generated is then condensed in the condenser (15) by cooling water flowing through the condenser tubes. The refrigerant water

condensed in the condenser and tube side of the low temperature generator is throttled and returned to the evaporator. The strong solution generated in the low temperature generator (16) is cooled down in the low temperature heat exchanger (17) and spread over the absorber tubes to complete the cycle.

Solid fuels always have some residual heat and in case of power failures or over firing conditions such residual heat can lead to crystallization of LiBr solution in the HTG itself. To prevent such malfunctioning, a dump condenser (22) is provided. In the dump condenser (22), cooling water is continuously flowing through the cooling tubes (23). Water vapor from the HTG condenses over the tubes and accumulates as liquid in the shell (24) of the dump condenser (22). The bottom of shell is connected to the HTG through a solenoid valve (27) and an isolation valve (28). The solenoid valve (27) is of NC type i.e. it opens only when electrical supply is cut off. When there is power failure, solenoid valve (28) opens and the liquid refrigerant accumulated in the shell is dumped in to LiBr solution in the HTG thus diluting it. This dilution takes care of the residual heat in the furnace and prevents possibility of crystallization of the LiBr solution.

Typically, the HTG design shown here has internal furnace and is having semi circular cum rectangular shape (cross section). HTG can also be of different type and shapes such as shell and tube with internal or external furnace / circular cross section / water tube type design where LiBr is on tube side. The tubes can be either plain or with fins.

The invention will now be described with respect to the following examples, which do not limit the invention in any way and only exemplify the invention.

Example 1

Vapor Absorption Machine of 100 TR capacity was manufactured with new proposed design of HTG. Along with system for firing solid fuels in the HTG. Following solid fuels were fired at firing rates varying from fuel as;

- Coconut shell ( 57 kg/hr)

- Wood pellets ( 62 kg/hr)

- Biomass pellets made from various agro wastes such as baggasse, saw dust etc. ( 85 kg/hr)

- Rice husk (106 kg/hr)

- Ground nut shells ( 90kg/hr)

- Wood waste ( 70 kg/hr)

- Coal (65 kg/hr)

The machine was operated to deliver approx. 100 TR (tons of refrigeration) refrigeration capacity at chilled water in / out temperatures at 12 / 6 ⁰ C. Cooling water temperatures were maintained at 32°C. The flue gas temperature at the entry of cyclonic separator was around 180 ⁰ C. The oxygen content in flue gas was at 9%.

Conditions were also created to simulate over firing and power failure separately as well as simultaneously. It was observed that there was no crystallization of LiBr in the machine under abnormal operating conditions and tests value were tabulated in table 1.

TABLE l

Conclusion

The above tests were carried out with dump condensers ON and it was observed that there was no crystallization in HTG even after power to the machine was switched off.

The tests were conducted without dump condenser also. The power to the machine was switched off and it was observed that the LiBr solution in the HTG crystallized after 2 hours of switching off of the power

Economic Significance:

Solid fuel is much cheaper as compared to liquid / gaseous fossil fuels.

Therefore, the operating cost of producing cooling effect reduces substantially.

Capital costs as compared to indirect solid fuel firing through conventional boiler route are typically 30-50% lower.

Operating costs as compared to indirect solid fuel firing through conventional boiler route are typically 5-10% lower.

Efficiency as compared to indirect solid fuel firing through conventional boiler route is typically 2% higher.

Power consumption as compared to indirect solid fuel firing through conventional boiler route is typically 5-10% lower.

While considerable emphasis has been placed herein on the specific structure of the preferred embodiment, it will be appreciated that many alterations can be made and that many modifications can be made in the preferred embodiment without departing from the principles of the invention. These and other changes in the preferred embodiment as well as other embodiments of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.