This document is a summary of the deliverableDC1.1, which explains the design of the pilot plant according to the specifications.
The first part of this deliverable collects the results obtained in the tests of CO2 dissolution in water, carried out in the laboratory. These tests have been performed using well water like the one to be used in the pilot facility, and supplied by EATOMIZADO partner of the project.
A specific laboratory equipment has been designed and built to carry out the tests. It consists of a column of water, in which gases are bubbled from the bottom of the column, by forcing them to pass through a porous solid. The gases bubbled consists of a controlled mixture of pure air and pure CO2 which comes from a cylinder. The CO2 concentration in the final mixture has been measured using a gas analyser.
The tests have been performed using gas streams with different CO2 contents (between 3 % and 100 % of the stream), with the aim of analysing how the gas composition affects the CO2 dissolution in water.
The results indicate that the quantity of CO2 dissolved in water is highly dependent on its concentration in the gas stream. It is expected that the CO2 content in the industrial gas stream will be around 2 - 3 %. For this concentration, a CO2 dissolution of 44 ppm is achieved.
The ratio between the volume of gases and the volume water obtained in the laboratory is 1.5. Nevertheless, this ratio is likely to increase in the pilot facility because the contact between gas and water may not be as homogenous as it is in the laboratory equipment.
The second part of the deliverable deals with the analysis of data from the last 5 years of the stack flue gases of the spray dryer that is going to be used in LIFE_FERTILIFE project. The average flow rate of the stack flue gases is 5857 Nm3/h, the temperature is around 78 ºC, and CO2 concentration is below 2%. The CO2 concentration in the flue gases of the stray-dryer is low because the supply of heat to the spray-dryer is done by the combustion of natural gas and usually the burner works with excess combustion air. In addition, the spray-dryer works in depression to facilitate the evaporation of the water, which facilitates the entrance of parasitic ambient air to it. This causes the flue gases to be diluted and have a low CO2 content.
Then, the results obtained in the laboratory and the stack flue gas analysis have been used to size the pilot equipment to be installed in EATOMIZADO This design is fully described in the last part of the deliverable and the main features are highlighted below.
In the initial proposal, it was planned to connect directly the pilot plant to the crop field through a pipeline and to pump the water from the industry to the field. However, during the project implementation, the way of transporting the water had to be changed, because it was not possible to install a pipeline between the pilot and the plot to be irrigated.
As a consequence, the carbonated water will be transported in lorries from the CO2 capture site (i.e. LIFE_FERTILIFE pilot plant) to the new selected crop field (named P2). Thus, the pilot plant has been designed considering that the carbonated water that is generated must be transported by means of deposits to the crop plot, leading to a different size and design than the one initially planned.
By agreement among all partners, it has been decided to design an equipment that allows bubbling the flue gases directly in the water tanks that will be used to transport the water to the citrus crop field. In this way, water transfer will be avoided and possible CO2 losses after its capture will be minimised.
Therefore, a flexible device consisting of a bubbling system connected to the flow diverted from the exhaust flue of the spray-dryer has been designed. By means of a blower, the gases are driven through the bubbling system, which remains submerged inside the tank filled with water, and the gases are bubbled through the water.
Thus, the pilot equipment will consist of a water tank, a blower and a water-gases diffusion system. The blower has the function of overcoming the pressure necessary to introduce the gases from the spray-dryer into the water tank through the diffusers. The selected diffusion system will consist of perforated cylinders, along their entire length, which have the following characteristics: high CO2 transfer in water to maximize its dissolution, due to the large number of bubbles produced, which leads to a high contact between gases and water. They will be easy to assemble and have a low maintenance cost, without obstruction problems and resistant to corrosion.
The volume of water to be treated is the one needed to irrigate the selected crop surface (about 2900 m2). This surface area is sufficiently representative for the study. The pH of the irrigation water should not be lower than 6.5.
The final amount of CO2 dissolved in water depends on multiple factors, which are both of chemical origin and of physical origin. Therefore, in order to maximize the dissolution of CO2 in water, the industrial prototype may incorporate some measures such as the cooling of the gas stream (if needed) before it comes in contact with the water, to prevent an excessive temperature increase of the water which would decrease the dissolution of CO2.
The tanks used to store and carry the water from the capture installation to the crop field will have a capacity of 1 m3. For the selected irrigation area, around 5 tanks of carbonated water will be needed daily. However, the actual working period of the CO2 capture pilot facility will depend on the usual irrigation plan established at the selected crop field (quantity of water and irrigation frequency, according to Annex 1).
The laboratory results show that the amount of CO2 captured with water will be small compared with the CO2 total emissions from the industrial facility. This is due to several factors, being prominent among them the low CO2 content in the industrial flue gas stream and the size of the pilot facility.