GB2467490A

GB2467490A - Reducing carbon dioxide emissions

Info

Publication number: GB2467490A
Application number: GB1008988A
Authority: GB
Inventors: Feng Xiong
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-05-28
Filing date: 2010-05-28
Publication date: 2010-08-04
Anticipated expiration: 2030-05-28
Also published as: GB2467490B; GB2467490A9; GB201008988D0

Abstract

A method of reducing carbon dioxide emission and coal consumption in a fossil fuel power plant by capturing exhaust carbon dioxide in an aqueous solution of algal species in a bioreactor, growing and harvesting the said algal species and using as substitution for fossil fuel (Figure 1). Advantageously the method has particular applications for effective harvesting of algal species from the aqueous solution, first through the use of a hydrodynamic vortex separator, in particular, integrated within the algal growth bioreactor (raceway type, Figure 2) then dewatering and drying of the separated algal species in a filter press using the heat recovered from the power plant exhaust. The method preferably further enhances the performance of algal separation in the hydrodynamic vortex separator and dewatering and drying by the use of fly ash as flocculating agent. Preferably the dried algal species is then reused as partial substitution to fossil fuel hence reducing proportionally the emission of carbon dioxide and the consumption of fossil fuel.

Description

Title: Method for Reducing Carbon Dioxide Emission and Fossil Fuel Consumption in Fossil Fuel Power Plant

Description: FIELD OF THE INVENTION

The present invention relates to the capture of C02 from the fossil fuel power plant exhaust for the growth of algae in aqueous solution, and the harvesting of the grown algae as substitution to the fossil fuel, hence reducing the emission of carbon dioxide and the consumption of fossil fuel.

BACKGROUND OF THE INVENTION

Algae have been grown in open pond race way bioreactor for the production of specialist commercial algae. Recently, considerable efforts have been made to grow algae for the production of transportation fuel -a new generation of biofuel, as the potential of algae for biofuel (productivity per land surface area) is significantly greater (30 x) than the current biofuel (such as corn derived ethanol, rapeseed oil derived biodiesel or palm based biofuel).

However the cost of harvesting algae from aqueous solution and the extraction of oil from harvested algae and conversion of extracted oil to biofuel has so far proven to be very expensive, as stated in "Opportunities and Challenges in Algae Biofuels Production -A position Paper by Dr. John R. Benemann, in line with Algae World 2008".

Existing algal harvesting methods include chemical coagulation/flocculation, filtration, centrifugation, entailing high cost of chemicals and energy demand.

The extraction of oil from the harvested algae is even more exotic, requiring high energy system to break the algal cells for the release of the oil content from the algae.

According to Dr Benemann, even at $1/litre of biofuel selling price, this would not be sufficient to cover the optismitic capital costs, let alone any operating costs.

One of the key feed stocks for the growth of algae is carbon dioxide, therefore algae production offers potential for the capture of man-made C02, specifically large coal fired power plant for the growth of algae and conversion to biofuel.

SUMMARY OF THE INVENTION

The Inventor has noted that current development and commercial efforts have been limited to the growth of algae for the production of transportation fuel -new generation biofuel, involving many complex process units (algal growth, harvesting, oil extraction, conversion to biofuel).

In addition, the Inventor has noted that current methods of harvesting algae from the growth media (various aqueous solutions) suffer from high capital and operational costs, such as coagulation/flocculation chemicals, centrifugation energy demand.

In the present invention, the algae are grown in a commercially proven open pond race way system, using the 002 from the fossil fuel power plant exhaust. The algae are then harvested using simple and proven systems long established in the water industry, such as hydrodynamic vortex separator, dewatering and drying filter press to produce a dry algae cake for direct use in power generation boiler (substitution to fossil fuel, specially solid fossil fuel). Therefore there is simultaneous reduction in the emission of 002 and fossil fuel consumption in the fossil fuel power plant.

The hydrodynamic vortex separator is simply integrated within the algal growth reactor (at one end of the open pond race way system).

In the present invention, a waste (by-product) from the fossil fuel power plant -the flyash, is reused in the algal harvesting processes (both the initial stage of algal separation -hydrodynamic vortex separator) and algal dewatering system to replace expensive chemical coagulant/flocculant and polymers that are employed in previous inventions and processes under development and commercialisation.

In the present invention, the heat source of the algal harvesting (drying process) is also the waste heat from the power plant exhaust. Therefore the heat content of the power plant exhaust is recovered as well as carbon dioxide and water content, greatly reducing the costs of the algal growth and harvesting costs.

In the present invention, the expensive oil extraction and biofuel conversion processes are not required, and the harvested algae are directly used to replace fossil fuel, leading to much great efficiency in reduction of 002 emission and consumption of fossil fuel.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 is a diagrammatic representation of the process of this invention for the growing and harvesting of algae, with the harvested algae (dried algae) used directly as replacement to the fossil fuel for power generation.

Figure 2 represents the integrated algal growth reactor and initial stage of algal harvesting (gravity separation/concentration of algae from aqueous solution).

Figure 3 represents one embodiment of the invention for the integrated algal growth reactor and initial stage of algal harvesting (gravity separation/concentration of algae from aqueous solution) where the circulation of the reactor is ensured with low head and high flow pumps and 002 absorption by diffusion of power plant exhaust gas (after heat recovery in the algae drying stage).

Figure 4 represents another embodiment of the invention for the integrated algal growth reactor and initial stage of algal harvesting (gravity separation/concentration of algae from aqueous solution) where the circulation of the reactor is supplemented by paddle wheels on the race way algal reactor.

DETAILED DESCRIPTION OF THE INVENTION

According to this invention represented in Figure 1, in its broadest aspect, the present invention provides a method of algae growth in a bioreactor (1) where returned water from the algal separation (2) and algal dewatering (3) is mixed with necessary make up water (such as wastewater) that also includes essential growth nutrients not recovered from the power plant exhaust gas.

The C02 required for the growth of algae is obtained from the power plant exhaust gas (after its residual heat is recovered during the algal drying stage (4). The 002 input to the algal bioreactor is via diffusion of the gas in the aqueous solution containing algae, which also serves as the circulation driving force of the bioreactor.

According to this invention represented in Figure 1, the waste by-products from the power plant -fly ash, is reused in this invention to improve the algal separation (2) and dewatering (3). The power plant hot exhaust (for example after the ESP -electrostatic precipitator) is first sent to the algal drying stage (4) for heat recovery then to the algae bioreactor for the recovery of 002 and water content so to minimise the need for water resource. The dried algae are sent directly to the power plant boiler as substitution fuel (at least partially) to the fossil fuel, particularly solid fossil fuel power plant.

According to this invention represented in Figure 2, one embodiment of the invention is the integrated bioreactor -open pond race way (6) and algal separator (5), particularly hydrodynamic vortex separator. The algal solution/medium is circulated in the direction (arrow marked) and enters the separator (hydrodynamic vortex) in a tangential flow (7). The concentrated algae solution is withdrawn from the bottom of the separator to further harvesting (dewatering and drying), and the algae depleted solution overflows back to the bioreactor.

According to this invention represented in Figure 3, the circulation of the content of bioreactor is ensured by a pump (11), especially a low head high flow Archimedes pump.

The fly ash for algal flocculation is dosed to the inlet of the pump for mixing and reaction with algae to enhance gravity separation of algae (settling in hydrodynamic vortex separator and flotation). 002 absorption in the algal solution is obtained by diffusion of power plant exhaust gas (9). The gas lift system (9) also supplements the circulation of solution in the bioreactor.

Downstream the gas lift compartment, additional section of the bioreactor (10) is designed to hold by a baffle the algae material separated via floatation from gas lift section (9).

Separated algal material (higher concentration than in the bioreactor) is collected from the bottom of the settling system (hydrodynamic vortex separator in this example) and skimmed off from the surface of the flotation section (as it is retained by the baffle). The concentrated algal material is then sent to the dewatering (3) and drying (4) systems to produce an algal cake for use directly as fuel to the power plant boiler, displacing at least partially the fossil fuel (such as coal).

Claims

Title: Method for Reducing Carbon Dioxide Emission and Fossil Fuel Consumption in Fossil Fuel Power Plant Claims: What I claim is: 1. A method of reducing the emission of carbon dioxide and coal consumption in the fossil fuel power plant by the capture of exhaust carbon dioxide in aqueous solution of algal species -algal bioreactor, the growth and harvesting of said algal species as substitution to the fossil fuel.
2. The method according to claim 1, wherein the initial stage of algal harvesting of algal species is through the use of a settling system, specifically hydrodynamic vortex separator and gas lift flotation to increase the algal concentration for further harvesting (second stage of dewatering and drying).
3. The method according to claim 1, wherein the growth and the initial stage of the harvesting of algal species are carried out in an integrated algal bioreactor (open pond race way) and hydrodynamic separator and gas lift flotation (shown in Figure 2).
4. The method according to claim 2, wherein the initial stage of the harvesting of algal species is further enhanced by the dosing of fly ash to the aqueous solution of algal species prior to the hydrodynamic vortex separator. Algal material that does not settle easily is allowed to separate from water by gas flotation downstream the settling system.
5. The method according to claim 3, wherein the circulation of the aqueous solution of algal species in the bioreactor -open pond race way is ensured by a pump, especially a low head high flow Archimedes pump. The fly ash is introduced to the inlet of the pump to enhance mixing between fly ash and algal material.
6. The method according to claim 3, wherein the circulation of the aqueous solution of algal species in the bioreactor is supplemented by a high flow and low lift pump or paddle wheel (Figure 4) prior to entry to the hydrodynamic vortex separator.
7. The method according to claim 1, wherein the second stage of the algal harvesting is the dewatering and drying of the concentrated algae material from initial stage of algal harvesting specifically the algal product from the hydrodynamic separator.
8. The method according to claim 7, wherein the heating source is the hot exhaust gas from the power plant, either directly or indirectly via hot water system.
9. The method according to claim 7, wherein the feed to the dewatering and drying system is dosed with fly ash from the power plant to enhance dewatering and drying performance.