Technical Field of the Present Invention

The present invention relates to a system and method for co-generation of heat and power from biomass using organic Rankine cycle (ORC). More specifically, the present invention relates to a system and method for co- generation of heat and power from animal waste, particularly poultry litter, comprising the steps of drying, pelletizing, combustion and energy generation.

Background of the Present Invention

During the growth of poultry bred and raised specifically for meat production (broilers), bedding consisting of material such as wood shavings, straw, hazelnut husks, corn cobs, shredded paper, rice hulls and volcanic ash is utilized. In time, excreta (manure) get mixed with the bedding. At the end of each production cycle, the bedding and manure mixture is cleaned out and replaced with fresh bedding for the new cycle. Broiler manure and bedding along with waste feed, dead birds, broken eggs and feathers are collected as waste, which will henceforth be referred to as poultry litter. On average 800 million broiler and layer chickens are produced in Turkey annularly. From there it can be estimated that, 10 million tons of poultry litter is produced annularly (Cayci et al., 1 ^st International Poultry Meat Congress, 2011). As a result of the increase in the number of broiler farms and broilers over the years, it has become important to address the issue of how to dispose of the waste produced by these farms, i.e. poultry litter. Poultry litter is predominantly composed of carbon (C) and water but it is also rich in nutrients such as, among others, nitrogen (N), phosphorus (P) and potassium (K), so it was traditionally utilized by land spreading on soil as a direct fertilizer. However, poultry litter causes problems of fly/insect menace and offensive odor particularly at high humid areas due to the high moisture content (70-80%) of poultry excreta. In addition, excess use of poultry litter as fertilizer may result in air, land and water pollution apart from spreading pathogenic organisms like salmonella and E. coli. The use of inorganic sources of phosphorus (P) in the diets of poultry which is reflected in poultry litter may also cause acceleration of eutrophication. Furthermore, as waste disposal is done periodically, during this time the waste slowly degenerates and produces ammonia, methane and carbon dioxide. Methane and carbon dioxide are a source of greenhouse gases and ammonia is a major noxious gas that is hazardous to birds and human health (Anupoju et al., 2015, Advances in Bioprocess Technology, pp.133-147). For these reasons, it has become imperative that alternative methods for poultry litter disposal are developed and utilized. Among these, composting, anaerobic digestion to obtain biogas and direct combustion to obtain combined heat and power (CHP) are the three most widely used methods. These methods have financial and environmental benefits in the form of sustainable energy generation and can also provide easier to handle fertilizer as a by-product (Kelleher et al., 2002, Bioresour. Technol., 83, pp. 27-36).

However, these methods also have some disadvantages. For example, the high moisture content of poultry litter makes it an ill-suited candidate for composting and it can also lead to ammonia emission and environmental pollution. On the other hand, poultry litter has a C/N ratio of 7 (Brodie et al., 1998, Composting in the Southeast: Proceedings of the 1998 Conference, pp. 65-76) due to its high ureic acid content; however, C/N values between 16- 25 are suitable for biogas production as this is the range that is more favorable for the growth of the bacteria population. Therefore, direct combustion emerges as the most advantageous method for poultry method disposal.

Co-generation of heat and power in a sustainable manner is possible by use of poultry litter as biofuel in a boiler. Heat produced by combustion is used to produce steam and electricity is generated by steam turbines utilizing said steam. Additionally, hot water produced by the process can be used for heating applications. Further, combustion produces an ash which retains most of the phosphate and potash present in the original litter and has a small and variable nitrogen content, which is advantageous. As the byproduct is more concentrated, sterile and easier to handle, its use is much more favorable than conventional poultry litter fertilizer (Dagnall, 1993, World's Poult. Sci. J., 49, pp. 175-177).

Nevertheless, there are also considerations to be taken into account for direct combustion of poultry litter. Poultry litter has a calorific value of 13.5 GJ/ton when air dried, which is approximately half that of coal. This calorific value decreases with increasing moisture and the moisture amount of poultry litter is variable for different broilers and at different stages of broiler development (Kelleher et al., 2002, Bioresour. Technol., 83, pp. 27-36). As poultry litter used for fuel is a mixture of the previous, it is important that poultry litter is homogenized by drying and preferably palletization before combustion.

Some examples of systems and methods of direct combustion of biomass, and poultry litter in particular, in the prior art are given below.

Patent document WO 2012/137010 (A2) discloses a method of operating a steam generation plant arranged burn a biomass fuel. The plant includes a boiler and a dump condenser system whereby moisture of the flue gas can be condensed and latent heat of condensation can be extracted by a dump cooler external to the flue gas path. This method utilizes a steam turbine powered by the generated steam to generate power; however, this has some disadvantages. For example, steam cycles require high operating pressures and temperatures which are costly and difficult to control. In addition, due to possible leaks, drainage or boiler blow-down, the system may constantly require ultrapure water that must be supplied with the use of a water- treatment system and a deaerator. It would be more advantageous to use an organic fluid with lower operating pressure and temperature demands as means for power generation. Additionally, unlike steam, organic fluids are non-eroding and non-corroding for valve seats, tubing and turbine blades.

Due to the costs involved, power generation plants utilizing steam are only economically viable at capacities of 10 MWe and above. As previously mentioned, biomass fuels have a smaller calorific value that that of fossil fuels, therefore a greater amount of biomass fuel is required to produce the required electrical power output. For this reason, animal waste has high transport costs as animal waste, such as poultry litter, must be collected from multiple farms and transported to and stored at the plant where it will be combusted. Organic Rankine cycle (ORC) is the most common system used for co- generation of heat and power from biomass using an organic working fluid. ORC is similar to a Steam Rankine Cycle and involves the same components as a conventional steam power plant: a boiler, a work producing expansion device, a condenser and a pump. However, the organic working fluid has a lower ebullition temperature than water, allowing power generation from low heat source temperatures. Also, the ORC process helps to overcome the relatively small amount of input fuel available because an ORC power plant can work efficiently in small scale (lower than 10 MW) and therefore excessive handling and the long-distance transport of poultry litter can be eliminated. Thus, ORC systems are suitable for biomass CHP applications (Quoilin et al., 2013, Renew. Sustainable Energy Rev., 22, pp. 168-186).

Patent document EP 2 545 254 (Bl) discloses an ORC system which is at least partially co-generative for production of electric energy and a hot fluid. The system contains a two cycles: one is ORC and the other is a vector fluid (thermal oil) cycle that transfers the heat from the boiler to the evaporator of ORC, in the manner of an indirect ORC system. The system also comprises at least two regenerative exchangers that use the heat of the organic fluid coming out of the turbine to heat the organic fluid leaving the pump and going into the evaporator, so that less heat is needed in the evaporator.

Patent document CN 104697239 (A) discloses a biomass-driven novel ORC combined cooling heating and power system. This system also employs an indirect ORC system. Depending on the demand for hot water, a fraction of the organic fluid leaving the turbine may be used to the organic fluid leaving the pump and going into the evaporator or may enter fully into the condenser. Additionally, the heat from the flue gas leaving the boiler is used to pre-heat inlet vector fluid and inlet air to conserve energy.

However, these systems don't disclose pretreatment operations for the biomass used, such as drying and palletization. As previously mentioned, poultry litter has a high moisture content and a heterogeneous structure and composition. Therefore, ensuring that the poultry litter is dry and therefore has a higher calorific value and has a uniform structure and composition is very important for efficient generation of heat and power. The present invention aims to improve on these shortcomings described in the prior art. The invention proposes a system and method for cogeneration of heat and power by combustion of animal waste, in particular poultry litter. The system contains a dryer and a pelletizer to obtain homogenized biofuel with a high calorific value from crude animal waste. Pelletized animal waste is transferred to a boiler to burn the animal waste and thermal oil is circulated through a heat exchanger in a flue stack of the boiler. Heated thermal oil is circulated through an organic Rankine Cycle for combined heat and power generation. Heated thermal oil is circulated through the evaporator of the organic Rankine Cycle system to vaporize an organic fluid and the vaporized organic fluid is circulated from the evaporator through a turbine to generate electricity. Expanded organic fluid leaving the turbine is condensed through a condenser by circulating water and heated water leaving the condenser may be used for heating the broiler farm and any dwellings nearby. The flue gas from combustion is used to dry animal waste in the dryer. The resulting ash from the combustion is suitable for use as a fertilizer.

The present invention provides a CHP system as provided by the characterizing features defined in Claim 1. Objects of the Present Invention

The object of the invention is to provide a system and method for co- generation of heat and power from animal waste, particularly from poultry litter, comprising the steps of drying, pelletizing, combustion and energy generation.

A further object of the invention is to provide a system and method for co- generation of heat and power from animal waste whereby the environmental concerns associated with crude animal waste is minimized by quick and efficient disposal thereof.

A further object of the invention is to provide a system and method for co- generation of heat and power from animal waste having a small scale electricity production capacity requiring a smaller amount of animal waste for operations, thereby reducing the costs of transport and preparation of crude animal waste.

A further object of the invention is to provide a system and method for co- generation of heat and power from animal waste, where the energy efficiency is increased by using the hot flue gas resulting from combustion for animal waste drying operations.

A further object of the invention is to provide a system and method for co- generation of heat and power from animal waste, where animal waste is pelletized to impart homogeneity and uniform structure thereto.

A further object of the invention is to provide a system and method for co- generation of heat and power from animal waste, whereby the calorific value of animal waste is increased by drying and animal waste is homogenized by peptization. A further object of the invention is to provide a system and method for co- generation of heat and power from animal waste using an organic Rankine Cycle (ORC) which is suitable for operating at low temperatures, pressures and flowrates and having a compact structure so that a plant for CHP from animal waste can be set up near an area of broiler farms and operated in a less costly manner.

A further object of the invention is to provide a system and method for co- generation of heat and power from animal waste where thermal oil is used as a heat transfer fluid instead of steam thereby minimizing the costs associated with steam usage such as pressure requirements and the need for compensating for loss of steam due to leakages in the process, commonly by production of ultrapure water.

A further object of the invention is to provide a system and method for co- generation of heat and power from animal waste, where harmful emissions are decreased due to lower combustion temperature requirements.

A further object of the invention is to provide a system and method for co- generation of heat and power from animal waste, where the energy efficiency is increased by using the generated heat for heating the broiler farm and any dwellings nearby. Brief Description of the Technical Drawings

Accompanying drawings are given solely for the purpose of exemplifying a CHP system, whose advantages over prior art were outlined above and will be explained in brief hereinafter.

The drawings are not meant to delimit the scope of protection as identified in the Claims, nor should they be referred to alone in an effort to interpret the scope identified in said Claims without recourse to the technical disclosure in the description of the present invention.

Figure 1 demonstrates a simplified diagrammatic view of a CHP system according to the present invention. Figure 2 demonstrates a simplified diagrammatic view of a part of an alternative embodiment of a CHP system containing a recuperator.

Detailed Description of the Present Invention

The following numerals are referred to in the detailed description present invention:

1 CHP system

2 Vector fluid circuit

3 Work fluid circuit

10 Boiler

11 Air preheater

12 Dryer 13 Pelletizer

14 Induced draft fan

15 Fan

16 Fabric filter

17 Ash collection means

20 Evaporator

21 ORC turbine

22 Condenser

23 Pump

24 Generator

25 Recuperator

30 Heated water

Figure 1 illustrates an embodiment of the present invention, referred to as CHP system (1). CHP system (1) comprises a vector fluid circuit (2), whereby the heat produced by boiler (10) is transferred to evaporator (20) of a work fluid circuit (3). Work fluid circuit (3) additionally comprises ORC turbine (21), condenser (22) and pump (23), all in fluid communication with each other. Work fluid circuit (3) serves two purposes: electricity production and heat production. Work fluid evaporated to superheated state in evaporator (20) passes through an ORC turbine (21) coupled to a generator (24) to produce electricity. After giving up most of its energy in ORC turbine (21), the work fluid is passed through condenser (22) whereby it is condensed into a liquid and circulated back into evaporator (20) by pump (23) completing work fluid circuit (3). Condenser (22) may be water-cooled. The cold water used in condenser (22) preferably comes from either a well or a municipal water supply. Hot water (30) produced by condenser (22) is preferably used for heating the broiler farm and any dwellings nearby. Condenser (22) could be a parallel plate condenser or a shell-and-tube condenser.

The work fluid utilized in work fluid circuit (3) is an organic work fluid. The organic work fluid is preferably a halocarbon refrigerant or a naturally occurring hydrocarbon. One of the advantages of using organic work fluids is that, unlike other working fluids such as water, they do not condense to a saturated condition after expansion but remain superheated even after losing a considerable portion of their energy during expansion. Furthermore, while water in the presence of oxygen can cause corrosion in the process components; there is no such issue with organic work fluids. In addition, organic work fluids have high vapor density, which lead to a lower volume flow rate and a more inexpensive system and high heat transfer properties so that maximum heat and power can be extracted from the fluid.

Work fluid circuit (3) operates under the principles of indirect ORC, meaning that the heat produced in boiler (10) by combustion of animal waste is not used for evaporation and superheating of work fluid directly, but is used for heating a vector fluid in a vector fluid circuit (2), which is then used to provide heat to evaporator (20). Vector fluid circuit (2) preferably utilizes thermal oil as vector fluid. Thermal oil has a high specific heat capacity that allows it to store a large amount of energy in a relatively small volume, and a high boiling point that allows it to remain in the liquid phase during heat exchange operations so that vector fluid circuit (2) does not have to contain components that are high pressure vessels.

Figure 2 illustrates an alternative embodiment of the present invention. In this embodiment a recuperator (25) may be added between ORC turbine (21) and condenser (22) so that additional heat can be extracted from the work fluid once the fluid has been expanded and used to preheat condensed work fluid before entering evaporator (20). Boiler (10) comprises a furnace where poultry litter is combusted. Before poultry litter is fed into boiler (10), it is passed through a dryer (12) to be dried so that its calorific value can increase. Dried poultry litter is then passed through a pelletizer (13) to obtain a uniform structure and composition of animal waste fuel. Pelletized poultry litter can also be stored safely if desired without the environmental concerns associated with crude poultry litter. Combustion air is preheated in air preheater (11) and fed into boiler (10) by fan (15).

Pelletized poultry litter is combusted on a moving grate in furnace of boiler (10). The use of a moving grate is advantageous as it can accommodate large quantities and variations of fuel composition and calorific value. After combustion, bottom ash is collected by ash collection means (17). Ash collection means (17) may be an ash collection auger. Boiler (10) also comprises a heat exchange unit so that the gaseous products of combustion can be used to heat thermal oil circulating in a heat exchanger unit in boiler (10). Hot flue gas is removed from boiler (10) by induced draft fan (14a) and ash is extracted from flue gas by fabric filter (16). On leaving fabric filter (16), flue gas is also used for drying crude animal waste in dryer (12). Alternatively, it can also be used as a heat source for heating combustion air in preheater (not pictured).

Bottom ash collected by ash collection means (17) and fly ash collected by fabric filter (16) are combined. As the resulting ash is more concentrated, sterile and easier to handle that crude poultry litter, it can easily be stored and transported to be used as fertilizer without the toxicity concerns associated with poultry litter.

In an alternative embodiment of the present invention, multi-cyclone dust collectors are used for collection of fly ash.

Dryer (12) may utilize any method of drying biomass known in the state of the art. Likewise, pelletizer (13) may also utilize any method of pelletizing biomass known in the state of the art.

The invention therefore proposes a CHP (combined heat and power) system (1) for co-generation of heat and power from animal waste by organic Rankine Cycle comprising: a boiler (10) for combustion of animal waste, a vector fluid circuit (2), whereby the heat produced by said boiler (10) is transferred to an evaporator (20) of a work fluid circuit (3), said work fluid circuit (3) operating under organic Rankine Cycle principals, at least one induced draft fan (14) for removing flue gases of combustion from boiler (10).

In one aspect of the present invention, said system (1) comprises a dryer (12) for drying of animal waste and a pelletizer (13) for homogenization of said dried animal waste wherein said dryer (12) and said pelletizer (13) are positioned in series on the path of animal waste feed and wherein said dryer (12) utilizes flue gases from boiler (10) removed by said at least one induced draft fan (14) for drying operations. In a further aspect of the present invention, said work fluid circuit (3) comprises an ORC turbine (21), a condenser (22) and a pump (23), all in fluid communication with each other. In a further aspect of the present invention, said ORC turbine (21) is coupled to a generator (24).

In a further aspect of the present invention, said condenser (22) is water cooled.

In a further aspect of the present invention, said condenser (22) is a parallel plate condenser.

In a further aspect of the present invention, said condenser (22) is a shell- and-tube condenser.

In a further aspect of the present invention, said work fluid circuit (3) comprises an organic work fluid. In a further aspect of the present invention, said organic work fluid a halocarbon refrigerant.

In a further aspect of the present invention, said organic work fluid a naturally occurring hydrocarbon.

In a further aspect of the present invention, said vector fluid circuit (2) comprises thermal oil. In a further aspect of the present invention, said work fluid circuit (3) comprises a recuperator (25) in fluid communication with said ORC turbine (21), said condenser (22) and said evaporator (20) whereby additional heat can be extracted from the work fluid once the fluid has been expanded and used to preheat condensed work fluid before entering evaporator (20).

In a further aspect of the present invention, said boiler (10) comprises a furnace. In a further aspect of the present invention, said furnace comprises a moving grate.

In a further aspect of the present invention, said system (1) comprises ash collection means (17) whereby the collection of bottom ash from combustion is facilitated.

In a further aspect of the present invention, said ash collection means (17) is an ash collection auger. In a further aspect of the present invention, said system (1) comprises a fabric filter (16) whereby the removal of fly ash from flue gases is facilitated.

In a further aspect of the present invention, said system (1) comprises a multi-cyclone dust collector whereby the removal of fly ash from flue gases is facilitated.

In a further aspect of the present invention, characterized in that poultry litter is usable as animal waste. In a further aspect of the present invention, a method for co-generation of heat and power from animal waste by organic Rankine Cycle is proposed, comprising the steps of: (a) using a dryer (12) to dry crude animal waste, (b) using a pelletizer (13) to obtain homogenized dry animal waste, (c) transferring pelletized dry animal waste to a boiler (10) to burn said animal waste and circulating thermal oil through a heat exchanger in a flue stack of the boiler (10), (d) circulating heated thermal oil through an evaporator (20) of the organic Rankine Cycle system to vaporize an organic fluid and circulating the vaporized organic fluid from the evaporator (20) through an ORC turbine (21) coupled to a generator (24) to generate electricity, (e) condensing the expanded organic fluid leaving ORC turbine (21) through a condenser (22) by circulating water and using the heated water leaving the condenser for heating the broiler farm and any dwellings nearby, (f) using the flue gas from combustion to dry animal waste in dryer (12).