The overall goal of this procedure is to determine an operational mode that reduces or even eliminates the recirculation of off-gas into the calciner in a calcium looping pilot plant. This method can help answer key questions in the calcium looping field, such as how to increase the energy needed in the calciner. The main advantage of this operational mode is that it reduces the size of the calciner as well as the amount of fuel and oxygen used.
To begin this procedure, use a mechanical shaker to sieve approximately 50 kilograms of limestone to the desired particle size distribution. Place the sieved materials in pots next to the calciner for feeding during the procedure. Next, start a low flow of nitrogen gas in the carbonator, calciner and the loop seals in the rotameters.
Turn on the carbonator transformers, manually. Set the temperatures of all carbonator electrical pre-heaters to 600 degrees Celsius. Begin acquiring data for temperature, pressure and gas composition in both reactors.
Then, turn on the calciner, gas pre-heaters. Set the heater around the calciner to 600 degrees Celsius, measuring inside the bubbling, fluidized bed, via a thermocouple. Open to calciner's top valve.
Add three liters of the sieved limestone into the downpipe and then close the top valve. After this, open the bottom valve so that the material flows into the reactor. Heat the material as outlined in the text protocol.
To begin, increase the flow of oxygen to increase the concentration in the calciner from zero to 40%volume. Make sure that the concentration is stable before starting the combustion. Next, use a rotameter to manually start the stoichiometric flow of natural gas.
Adjust the rotameter for the natural gas flow to increase the oxygen concentration in the calciner in 20%increments, until 100%oxygen concentration, natural gas combustion is achieved. After this, add seven liters of limestone to the fluidized bed in 0.5 liters increments. Then, increase the flow of nitrogen gas in the carbonator to start the circulation.
Calcine all of the material, as outlined in the text protocol before starting carbon dioxide capture. To begin, use the rotatmeter to manually, switch the carbonation gas from nitrogen to 15%volume carbon dioxide. Using the rotameters, manually adjust the flow of natural gas and oxygen to the calciner, until a stable temperature of between 930 and 950 degrees Celsius is achieved.
When the material's activity begins to decline, add more limestone. To begin the shut-down procedure, use the rotameter to manually turn off the natural gas flow. Slowly, decrease the flow of oxygen, until it is shut off, then switch the gases in both reactions to nitrogen.
Turn off all heaters and let the rig cool overnight. The reactors have to cool overnight to reach room temperature. In this study, a plant comprised of two interconnected, fluidized beds is used to test the process of running from 20%oxygen to 100%oxygen at the calciner inlet.
The rig is first tested with 30%oxygen and the limestone fraction between 200 and 300 micrometers circulating between the two reactors. The inferior capture efficiency of 45%is mainly due to there being insufficient heat to calcine all of the limestone in the bubbling fluidized bed. This causes a decrease in the ratio of calcium oxide to calcium carbonate in the carbonator feed.
The rig is then tested with 100%oxygen and a limestone fraction of 100 to 200 micrometers. Most of the limestone material ended up in the calciner cyclone. This is likely the cause of the low capture efficiency and suggests that smaller limestone particles do not provide a beneficial effect on system performance.
Lastly, the rig is tested with 100%oxygen, a limestone fraction between 300 and 400 micrometers and careful control over the heat and limestone content. As can be seen, a stable capture efficiency of approximately 70%is achieved for over three hours. Thus, it can be determined that a stable run can be achieved with optimized conditions.
After it's development, this technique paved the way for researchers in the field of carbon capture to test the calcium looping cycle with high oxygen concentrations in the calciner. After watching this video, you should have a good understanding of how to perform an experiment, running with high oxygen concentrations in the calciner. Don't forget that working with high oxygen concentrations can be extremely hazardous and precautions, such as turning off the gas if combustion is not occurring properly should always be taken while performing this procedure.
