SYSTEM AND METHOD FOR BALANCING LOAD IN POWER BLOCKS

BACKGROUND

[0001] The invention relates generally to power blocks and, more
specifically, to a system and method for balancing load in a power block.

[0002] The cost of electricity generated by renewable energy technologies is not always higher than electricity generated by fossil fuel sources. In certain rural areas, expensive back-up power options such as diesel generators are often the source of power due to poor grid quality. Variable loads in islanded conditions result in inefficient operation of diesel generators. Even when grid power is available, the actual cost of power at the point of consumption is very high largely because of line losses in transmission and distribution. Power from biomass gasifier based plants is a less expensive alternative in such rural areas.

[0003] Biomass materials such as firewood and agro-residues mostly include carbon, hydrogen, and oxygen along with some amount moisture and ash. Under controlled conditions characterized by low oxygen supply and high temperatures, most of the biomass materials may be converted into gaseous fuel known as "producer gas," which includes carbon monoxide, hydrogen, carbon dioxide, methane, and nitrogen. This gas has a lower calorific value than natural gas or liquefied petroleum gas but may be burnt with high efficiency and a certain degree of control without emitting smoke. However, islanded operation of biomass systems tends to result in poor power quality and frequent trips. Trips may occur when power demand is less than the power generated.

[0004] It would be useful to have a biomass-based power generation system capable of balancing load demands and efficiently dealing with waste materials.

BRIEF DESCRIPTION

[0005] In accordance with one exemplary embodiment disclosed herein, a method for load balancing is disclosed. The method includes reacting a biomass material to produce a gaseous product and removing contaminant materials from the gaseous product to produce a clean gaseous fuel. The clean gaseous fuel is used to generate electric power. At least some of the generated electric power is supplied to a load. When a power demand of the load is less than the generated electric power, a remaining portion of the generated electric power is fed to a load balancing unit.

[0006] In accordance with another exemplary embodiment disclosed herein, a power generation system is disclosed. The power generation system includes an energy source configured for generating electric power, a load configured for receiving at least some of the generated electric power; and a water treatment unit. A control system is configured for load balancing by, when a power demand of the load is less than the generated electric power, generating control signals commanding the energy source to feed at least some of the remaining portion of the generated electric power to the water treatment unit.

[0007] In accordance with another exemplary embodiment disclosed
herein, a control system for load balancing in a plurality of power blocks is disclosed. The control system includes a plurality of unit controllers in each power block. Each unit controller is coupled to a respective unit of the energy source. A supervisory controller is coupled to the respective unit controllers. A system-level controller is coupled to the supervisory controller of each power block. The supervisory controller is configured for load balancing in each power block when a power demand of the load is less than the generated electric power. A system-level controller coupled to the supervisory controller of each power block; wherein the system-level controller is configured for load balancing across the plurality of power blocks.

DRAWINGS

[0008] These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

[0009] FIG. 1 is a diagrammatical representation of a power block having a
control system for balancing load in the power block in accordance with an exemplary embodiment of disclosed herein;

[0010] FIG. 2 is a diagrammatical view of a power block having a gasifier
and a control system for balancing load in the power block in accordance with an exemplary embodiment disclosed herein;

[0011] FIG. 3 is a diagrammatical view of a power block having an anaerobic digester and a control system for balancing load in the power block in accordance with an exemplary embodiment disclosed herein; and

[0012] FIG. 4 is a diagrammatical representation of a plurality of control
systems, each provided for a respective power block in accordance with an exemplary embodiment disclosed herein.

DETAILED DESCRIPTION

[0013] As discussed in detail below, embodiments of the present invention
provide methods for balancing load. In one embodiment, the method includes reacting a biomass material to produce a gaseous product. Contaminant materials in the gaseous product are removed to produce a clean gaseous fuel. The clean gaseous fuel is used by a power generation unit to generate electric power. At least some of the generated electric power is fed to a load. When a power demand of the load is less than the generated electric power, a remaining portion of the generated electric power is fed to a load balancing unit. In certain other exemplary embodiments, a power generation system is disclosed. In certain other exemplary embodiments, a control system for load balancing in a plurality of power blocks is disclosed. The exemplary system and method is used to generate electric power from renewable energy sources such as biomass. The exemplary system and method may be used to generate clean water from brackish water. In such embodiments, a load balancing unit, e.g. a water treatment unit, is used for load balancing.

[0014] Referring to FIG. 1, a power block (or "power generation system")
10 is illustrated in accordance with an exemplary embodiment disclosed herein. The system 10 includes an energy source 12 configured for generating electric power. A main load 14 is configured for receiving at least some portion of the generated electric power from the energy source 12. In some embodiments, the energy source 12 may be a renewable energy source, e.g. biomass energy source, wind energy source, photovoltaic energy source, or combinations thereof. In the illustrated embodiment, the energy source 12 is also coupled to a load balancing unit 16 and a thermal load 18. In some embodiments, the load balancing unit 16 is a water treatment unit. A control system 20 is coupled to the energy source 12, the load balancing unit 16, and configured for load balancing in the power block 10. When a power demand of the main load 14 is less than the generated electric power, the control system 20 generates control signals commanding the energy source 12 to feed at least some of the remaining (excess) portion of the generated electric power to the load balancing unit 16. The load balancing unit 16 is employed as an electrical load to balance electrical load fluctuations, enabling operation at constant load, and maintaining overall higher efficiency and constant output frequency. In one embodiment, the power block 10 is rated at about 650KW. In another embodiment, multiple such power blocks 10 may be coupled in parallel and used in a coordinated manner to provide a larger system (such as rated at about 5MW, for example). In some embodiments, the power blocks may be used to generate power for applications including rural industrial applications, rural domestic applications, refrigeration for agricultural products, communication services, irrigation/pumping, or the like. The exemplary power block may be grid connected or may be operated in an islanded condition.

[0015] Referring to FIG. 2, an exemplary power block 10 is illustrated. As discussed above, the system 10 includes the energy source 12 configured for generating electric power. In the illustrated embodiment, the energy source 12 includes a gasifier 22, a cleaning unit 24, and a power generation unit 26. A biomass feedstock (dry biomass) is fed to the gasifier 22. The dry biomass may include woody biomass, or agricultural waste such as rice/oat husk. Preprocessing of biomass such as sizing and drying may be required to satisfy feedstock size and moisture requirements to achieve and maintain efficient performance of the gasifier. The dry biomass is subjected to partial oxidation in the gasifier 22 to produce a gaseous product. In the illustrated embodiment, the gaseous product is a synthetic gas (producer gas). The synthetic gas is fed to the gas cleaning unit 24 to remove contaminant materials such as ash particles, tar, alkalis, or the like from the synthetic gas to produce a clean gaseous fuel. In some embodiments, the gas cleaning unit 24 is a basic gas cleaning unit including a cyclone separator, raw and chilled water cooler, fabric filter, or the like. In certain other embodiments, the gas cleaning unit 24 is an advanced gas cleaning unit employing sorbent or membrane based gas cleaning unit.

[0016] The clean gaseous fuel is fed to the power generation unit 26 for generating electric power, and also thermal energy. In the illustrated embodiment, the power generation unit 26 may include an engine and a generator (not shown). In certain other embodiments, the power generation unit 26 may include micro turbines, steam turbines, fuel cells, or the like. In some embodiments, the rating of power generation unit 26 may be in the range from about 0.3 MW to 3 MW. At least some portion of the generated electric power is fed from the power generation unit 26 to the main load 14 via a power distribution unit 28. The thermal energy may be in the form of heated water, approximately at about 90 degrees Celsius. The thermal energy may optionally be fed to the thermal load 18. Several examples of thermal loads include household heaters, absorption chiller based cold storage units, multi-stage flash units for thermal water desalination, or the like. The specification parameters of the illustrated gasifier 22 including biomass feed rate, gas flow rate from the gasifier, characteristics of feed stock, average calorific value of gas produced from gasifier, gas composition, and gasification efficiency may vary depending upon the application.

[0017] When available, a portion of the generated electric power is fed to
the load balancing unit 16. In the illustrated embodiment, the load balancing unit 16 is a water treatment unit and may include a reverse osmosis system, an electro dialysis reversal system, an ultra-filtration membrane, or combinations thereof. In some embodiments, the water treatment unit is configured to treat waste water and produce potable water. In certain other embodiments, the water treatment unit is configured to treat brackish water. When a power demand of the main load is less than the generated electric power, a remaining portion (excess portion) of the generated electric power is fed to the load balancing unit 16 via the power distribution unit 28. In some embodiments, the generated electric power may be temporarily stored in a power storage unit 30 before being fed to the main load 14, or the load balancing unit 16. The individual operational details of the gasifier, 22, gas cleaning unit 24, and power generation unit 26 are known to those skilled in the art.

[0018] The control system 20 is coupled to the energy source 12, load balancing unit 16, and the power distribution unit 28 and configured for load balancing in the power block 10. As discussed above, when a power demand of the main load 14 is less than the generated electric power, the control system 20 generates control signals commanding the energy source 12 to feed at least some of the remaining (excess) portion of the generated electric power to the load balancing unit 16 via the power distribution unit 28. In the illustrated embodiment, the control system 20 includes a first unit controller 32, a second unit controller 34, a third unit controller 36, a fourth unit controller 38, and a fifth unit controller 37 coupled respectively to the gasifier 22, the gas cleaning unit 24, the power generation unit 26, the load balancing unit 16, and the power distribution unit 28.

[0019] The first unit controller 32 is configured to monitor and control gasifier parameters including biomass feed rate into the gasifier, gas flow rate from the gasifier, characteristics of feedstock, average calorific value of gas, gas composition, temperature and pressure at various gasifier locations, and gasification efficiency within predefined limits. The second unit controller 34 is configured to monitor and control gas cleaning unit parameters including gas temperature, relative gas moisture, gas condensate, dust particles in gas, silicon content in gas, and gas contaminants within specified limits based on type of gasifier and feedstock. The third unit controller 36 is configured to monitor and control power generation unit parameters including lower heating value of fuel gas, electrical output, engine efficiency, and thermal efficiency within specified limits. The fourth unit controller 38 is configured to monitor and control water treatment unit parameters including amount of dissolved solids in feed water, acid content in water, amount of pure water recovered, power consumption, and water contaminants such as iron, manganese, aluminum, hydrogen sulfide, turbidity, or the like within specified limits. The fifth unit controller 37 is configured to monitor and control the power distribution unit 28.

[0020] In the illustrated embodiment, the control system 20 further includes a supervisory controller 40 coupled to the unit controllers 32, 34, 36, 37, and 38 and configured to control the unit controllers 32, 34, 36, 37, and 38 for coordinated power block control of the gasifier 22, gas cleaning unit 24, power generation unit 26, power distribution unit 28, and the load balancing unit 16. The supervisory controller 40 is coupled to a remote monitoring unit 42 configured to log data from the power block and to enable remote monitoring of health and performance of the power block. It should be noted herein that the illustrated power block may either be coupled to a utility grid or operated in an islanded condition. In some embodiments, the power block may be optionally provided with a metering system for monitoring power consumption from the power block.

[0021] In the illustrated embodiment, the supervisory controller 40 may further include a database 44, an algorithm 46, and a data analysis block 48. The database 44 may be configured to store predefined information about the power block 10. For example, the database 44 may store information relating to gasifier parameters, gas cleaning unit parameters, power generation unit parameters, load balancing unit parameters, main load and thermal load specifications, or the like. The database 44 may also include instruction sets, maps, lookup tables, variables, or the like. Such maps, lookup tables, instruction sets, are operative to correlate characteristics of the gasifier 22, gas cleaning unit 24, power generation unit 26, load balancing unit 16, main load 14, and thermal load 18, with the generated power and the power demand. Furthermore, the database 44 may be configured to store actual ensed detected information from the above-mentioned unit controllers 32, 34, 36, 37, and 38. The algorithm 46 facilitates the processing of signals from the above-mentioned unit controllers 32, 34, 36, 37, and 38.

[0022] The data analysis block 48 may include a variety of circuitry types, such as a microprocessor, a programmable logic controller, a logic module, etc. The data analysis block 48 in combination with the algorithm 46 may be used to perform the various computational operations relating to determination of various unit parameters, amount of electric power generated, electric power demand, thermal power demand, or combinations thereof. Any of the above mentioned parameters may be selectively and/or dynamically adapted or altered relative to time.

[0023] Referring to FIG. 3, another exemplary power block 10 is illustrated. In the illustrated embodiment, the energy source 12 includes an anaerobic digester 50, the cleaning unit 24, and the power generation unit 26. A biomass feedstock (wet biomass) is fed to the anaerobic digester 50. The wet biomass may include animal waste, agricultural waste, food waste, or the like. The biomass may be subjected to dilution and pretreatment before being fed to the digester 50. The wet biomass is subjected to reaction in the anaerobic digester 50 to produce a gaseous product. In the illustrated embodiment, the gaseous product is a biogas. The biogas is fed to the gas cleaning unit 24 to remove contaminants such as hydrogen sulfide from the biogas to produce a clean gaseous fuel. In some embodiments, the gas cleaning unit 24 is a methane gas cleaning system and may typically involve hydrogen sulfide scrubbing.

[0024] As discussed in the previous embodiment, the clean gaseous fuel is fed to the power generation unit 26 for generating electric power, and optionally also thermal energy. At least some portion of the generated electric power is fed from the power generation unit 26 to the main load 14 via the power distribution unit 28. The thermal energy is fed to the thermal load 18. When available, a portion of the generated electric power is fed to the load balancing unit 16. In the illustrated embodiment, the load balancing unit 16 is a water treatment unit and may include reverse osmosis system, an electro dialysis reversal system, ultra filtration membrane, or combinations thereof. In certain other embodiments, the water treatment unit is configured to treat brackish water.

[0025] The control system 20 is coupled to the energy source 12, load balancing unit, the power distribution unit 28, and configured for load balancing in the power block 10. As discussed above, when a power demand of the main load 14 is less than the generated electric power, the control system 20 generates control signals commanding the energy source 12 to feed at least some of the remaining (excess) portion of the generated electric power to the load balancing unit 16 via the power distribution unit 28. In one embodiment, if the amount of generated electric power is "X" units and power demand is "Y" units, and if the power demand "Y" is less than the amount of generated electric power "X", then the remaining portion of generated electric power "X-Y" units is fed to the load balancing unit 16. In the illustrated embodiment, the structural details and operation of the control system 20 is similar to that described in the previous embodiment.

[0026] It should be noted herein that even though the above described embodiments are explained with reference to gasifier and anaerobic digester, it should not be construed any way as limiting the scope. Other types of suitable energy sources are also envisaged. In one example, biomass material may be subjected to combustion in a combustion unit and steam generated from combustion is fed to a steam turbine employed as a power generation unit for generating power.

[0027] Referring to FIG. 4, a plurality of exemplary control systems 20, each provided for a respective power block 10, is illustrated. Each control system 20 includes a plurality of unit controllers such as, for the embodiments of FIGs. 2 and 3, the first unit controller 32, the second unit controller 34, the third unit controller 36, the fourth unit controller 38, and fifth unit controller 37 coupled respectively to the gasifier/anaerobic digester, the gas cleaning unit, the power generation unit, the load balancing unit, and the power distribution unit. Each control system 20 further includes the supervisory controller 40 coupled to the unit controllers 32, 34, 36, 37, and 38 and configured to control the unit controllers 32, 34, 36, 37, and 38 for coordinated power block control. As discussed in the previous embodiments, when a power demand of the main load of one power block is less than the generated electric power of the respective power block, the respective control system 20 generates control signals commanding the energy source to feed at least some of the remaining (excess) portion of the generated electric power to the load balancing unit.

[0028] In the illustrated embodiment, each of the supervisory controllers 40
is coupled to a system-level controller 52. The system-level controller 52 is configured for load balancing across the plurality of power blocks. For example, when a power demand is less than the generated electric power in one power block and power availability in another power block is not sufficient, the system-level control may provide control signals to feed at least some of the remaining portion of the generated electric power of the one power block to the other block. In other words, the system-level controller 52 controls the sharing of electric power between power blocks. The exemplary control system facilitates power sharing between multiple such power blocks. The supervisory controller 40 is coupled to the remote monitoring unit 42 configured to log data from the power blocks and to enable remote monitoring of health and performance of the power blocks. The remote monitoring unit 42 enables a user to be informed of problems associated with power blocks, to remotely log into the system to identify associated problems, and to fix the problems remotely. Suitable alarm generation may also be provided. This facilitates protection of the power blocks against unbalanced loading and variation in grid voltage/frequency.

[0029] While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

WE CLAIM

1. A method for balancing load, comprising:
reacting a biomass material to produce a gaseous product;

removing contaminant materials from the gaseous product to produce a clean gaseous fuel;

using the clean gaseous fuel to generate electric power;

supplying at least some of the generated electric power to a load;

when a power demand of the load is less than the generated electric power, feeding at least some of the remaining portion of the generated electric power to a load balancing unit.

2. The method of claim 1, wherein the load balancing unit comprises a water treatment unit.

3. The method of claim 2, comprising reacting a biomass material in a gasifier.

4. The method of claim 2, comprising reacting a biomass material in an anaerobic digester.

5. The method of claim 2, further comprising using the water treatment unit to treat brackish water.

6. The method of claim 1, wherein using the clean gaseous fuel to generate electric power results in generation of heated water, and further comprising feeding the heated water to a thermal load.

7. The method of claim 1, wherein the load is not coupled to a utility grid.

8. A power generation system comprising:

an energy source configured for generating electric power;

a load configured for receiving at least some of the generated electric power;

a water treatment unit; and

a control system configured for load balancing by, when a power demand of the load is less than the generated electric power, generating control signals commanding the energy source to feed at least some of the remaining portion of the generated electric power to the water treatment unit.

9. The system of claim 8, wherein the water treatment unit comprises a reverse osmosis system, an electro dialysis reversal system, or combinations thereof.

10. The system of claim 8, wherein the energy source comprises a biomass energy source configured to react a biomass material resulting in generation of heated water.

11. The system of claim 10, wherein the control system further comprising a supervisory controller coupled to a plurality of unit controllers, each unit controller coupled to a respective unit of the biomass energy source.

12. The system of claim 10, further comprising a thermal load, wherein the biomass energy source is configured to supply heated water to the thermal load.

13. The system of claim 8, wherein the power generation system comprises an islanded system.

14. A control system for load balancing in a plurality of power blocks, each power block comprising an energy source, a load, and a water treatment unit, the control system comprising:

for each power block, a plurality of unit controllers, each unit controller coupled to a respective unit of the respective power block, and a supervisory controller coupled to the respective unit controllers, wherein the supervisory controller is configured for load balancing in each power block when a power demand of the load is less than the generated electric power, and a system-level controller coupled to the supervisory controller of each power block;

wherein the system-level controller is configured for load balancing across the plurality of power blocks.

15. The system of claim 14, wherein the system-level controller is configured for load balancing across the plurality of power blocks when a power demand is less than the generated electric power of one power block by generating control signals to feed at least some of the remaining portion of the generated electric power of the one power block to other block.

16. The system of claim 15, wherein the system-level controller is configured to generate control signals to feed at least some of the remaining portion of the generated electric power of the one power block to the load, water treatment unit, or a combination thereof of the other power block.

17. The system of claim 14, wherein each unit controller is coupled to the respective unit of the energy source comprising a biomass energy source of the respective power block.

18. The system of claim 14, wherein the supervisory controller is configured load balancing in each power block when a power demand of the load is less than the generated electric power, by generating control signals commanding the energy source to feed at least some portion of the generated electric power to the water treatment unit comprising a reverse osmosis system, an electro dialysis reversal system, or combinations thereof of the respective power block.