Patent Application
20140342443
The subject of this application relates generally to production of algae and more specifically to a system and method for production of algae.
The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides practical illustrations for implementing exemplary embodiments of the invention.
Referring to
As sunlight travels through algae containing liquids, the light is absorbed by the algae. The depth of algae culture through which sunlight will penetrate depends on the concentration of the algae in the solution. The diameter of the tubes is chosen to maximize the algae production per unit of capital invested. For some algae cultures, sunlight only penetrates about one inch past the surface, In some algae cultures, the optimum tube size is about two inch inside diameter. In larger diameter tubes, all of the incident sunlight is absorbed by the algae before the light can penetrate to the center of the tube. Smaller diameter tubes have higher capital cost per unit of algae production and higher pumping energy cost.
The arrays of tubes are enclosed in a structure with roof panels and apertures. The roof panels may be sloped downward towards the north at 45 degrees. The roof panels may be made of concrete or other structural material. Between adjacent roof panels, apertures are positioned to allow sun light to enter. The apertures are made of a translucent or transparent material such as glass a plastic like Plexiglas,
During algae production, water, algae, nutrients, and a carbon dioxide carrier such as sodium bicarbonate, are introduced into the tubes. These may be introduced from ancillary sources, e.g., containers or dispensers on site. For example, in some applications, carbon dioxide may be collected from a carbon dioxide scrubber and directed to the PBR. Nutrients may be purchased from and delivered by vendors or may be received as a by-product from other process streams or systems.
The rood panels are designed to provide shade in the summer to avoid overheating the enclosures during hot weather. The apertures are fitted with insulating curtains which are mechanically, electrically, or pneumatically operated. Insulating curtains are positioned against the inside of the apertures during hot or cold weather to maintain the temperature within the enclosure within the range in which algae grows. The curtains are moved away from the apertures during daylight hours to admit sunlight. At night during cold weather, the curtains are positioned against the apertures to reduce heat loss. On hot days, the curtains may be positioned against the apertures during portions of the day to reduce heat gain within the enclosure.
In the embodiment illustrated in
Algae grow best with sunlight that is not as intense as continuous, direct sunlight. An example is Spirulina which grows best in light that has an average intensity of between 10% and 20% of full sunlight. Algae is known to grow faster when subjected to light/dark cycles that occur at a frequency of greater than one cycle per second. Some of the tubes in the PBR may be coated with opaque rings at intervals to provide an average light intensity which is particularly suited to the algae strain chosen for the PBR. An example of an exemplary embodiment is the top three layers of tubes are painted with a series of bright white rings one inch wide and ¼ inch apart. Sunlight enters the tubes along 20% of the length of the tubes, At velocities of more than twenty feet per minute, the algae in the solution passing through the tubes experiences light/dark cycles with a frequency of about four cycles per second. In the layers of tubes below the first three layers, light intensity is greater than it would otherwise be due to the light that has been reflected from the bright white painted rings above. The fourth, fifth, and sixth layers of tubes from the top of the array may have painted rings that are ¾ inch wide spaced inch apart. Sunlight that is primarily reflected light which is less intense that direct sunlight, enters the tubes along 60% of the length of the tubes. Algae experiences light/dark cycles with a frequency of about four cycles per second. The optimum width and spacing of painted rings is chosen taking into account the latitude of the site, the algae strain in the culture, and the average weather conditions.
Galleries may be disposed on opposing ends of the tubes and positioned at intervals along the length of the tubes. The galleries contain tanks, at least one sending tank and at least one receiving tank. Some of the tanks are equipped with pumps to facilitate circulation of algae and water through the tubes. Any pump suitable for moving algae containing liquids may be used. An example of a suitable pump is an auger style pump.
The galleries may include a device to de-oxygenate the algae containing liquid, As algae grow, it absorbs carbon dioxide and releases oxygen. As the concentration of oxygen increases, it will become toxic to the algae. At intervals along the length of the tubes, the oxygen must be vented. An oxygen venting arrangement may be built into the tanks. One example of such an arrangement is a tank with a receiving side and a sending side. Tubes bringing algae containing liquids terminate at pipe nipples protruding from the receiving side. The algae containing liquid flows from the tubes into pipe nipples protruding from the receiving side of the tank, up towards the top of the tank, horizontally across a shallow flow path, down into the sending side of the tank, and out pipe nipples protruding from the sending side of the tank. Oxygen is vented from the liquid as it flows across the shallow flow path.
Venting may be improved by bubbling air or oxygen up through the liquid as it flows across the shallow flow path. Pumping energy is minimized by bubbling air under a shallow stream of water. The oxygen vented from the top of the tanks may be vented to atmosphere, or it may be captured for a variety of uses. One such use would be to gasify coal in a power plant.
Variations on the PBR are described below, including construction techniques and ancillary systems and equipment that may be part of a larger integrated facility system and process.
In various embodiments of the invention, the PBR may further include, be configured with, or connected to solar concentrators, seasonal geothermal storage components and cycles, galleries; head tanks, and special pumps, algae and water circulation patterns, and water conservation systems or features, e.g. the PBR may operate as a dry cooling tower. It should be understood that the dimensions and specifications of various systems, components; and parameters are illustrative and they may be varied as design choice or process or economic efficiencies require.
WATER and ALGAE CIRCULATION PATTERN
The temperature of the PBR is kept high enough for the algae to grow in the winter by using waste heat, tor example waste heat from a power plant that is normally dispersed into the atmosphere with a cooling tower. The PBR will conserve water that otherwise is used in an evaporative cooling tower to remove the heat. The PBR then serves as a dry cooling tower.
The concentration of sodium bi-carbonate will typically vary between locations in the PBR. The maximum sodium bi-carbonate concentration will occur at the scrubber outlet. As this solution is introduced into the PBR it will be diluted to the “operating” level. The concentration will highest the morning. During the day, the concentration will decrease as the algae consume carbon dioxide at a rate higher than it is being delivered from the scrubbers. During the night, the concentration will rise as more carbon dioxide is delivered while the algae are dormant. As algae consume carbon dioxide, sodium bi-carbonate is converted to sodium carbonate. In the carbon dioxide scrubber, the sodium carbonate is converted back into sodium bi-carbonate.
WATER CONSERVATION FEATURES Dry Cooling Tower
The sensible heat demand associated with a PER that is integrated with a power plant according to embodiments of the invention may require 100% of the heat rejected from the plant's turbine generator condenser/circulating water system plus the maximum that is reasonably available in the plant's flue gas during much of the year. The PER may not be able to absorb all of this heat during hot summer weather in which case the excess waste heat will be rejected through the cooling tower system.
This sensible heat rejection inherently available in the invention creates three primary Water Conservation Features.
In the foregoing detailed description, the invention has been described with reference to specific embodiments. However, various modifications and changes can be made without departing from the scope of the invention as set forth in the appended claims.
