(281c) Pilot Plant Evaluation Featuring High Temperature PSA-Oxygen Using Perovskite-Type Oxygen Adsorbent

As described in the previous report on pressure swing adsorption using perovskite-type oxygen adsorbent, oxygen/nitrogen separation from air at high temperature (HTPSA-O₂) shows substantial reduction in the electric power consumption rate.

In this study, we built a 5m³N-O2 / h pilot plant as a step towards adoption for practical use. At high temperatures in the range of 500-800 degrees Celsius, 1) the heating method for the adsorption tower, 2) temperature control, and 3) the optimum temperature for HTPSA-O2 were considered during investigation of power consumption reduction by heat recovery.

In particular, in order to achieve a higher heat recovery ratio, the front and rear parts of the adsorption tower are filled with the heat storage material, and in the adsorption step (Step 11) of the first cycle, the feed air is supplied from the front part to contact with the heat storage material for heat exchange between the feed air and the desorbed oxygen. The lack of heat content is compensated for by means of an electric heater. Given that effluent nitrogen comes into contact with the heat storage material at the rear part of the adsorption tower, the heat in the nitrogen can be recovered. In the desorption step (Step 12), since the recovered oxygen comes into contact with the heat storage material in the front part, the heat in the desorbed oxygen can be recovered.

In the next (second) cycle, by supplying the feed air from the rear part of the tower in the adsorption step (Step 21), the feed air contacts the heat storage material in the rear part and heat exchange between the feed and the heat storage material proceeds. Heat insufficiency is again supplemented by an electric heater. The heat in the effluent can be recovered with the heat storage material in the front part. Heat recovery from the desorbed oxygen can be undertaken with the heat storage material in the rear part in the desorption step (Step 22).

For each cycle, the directions of the feed air and the desorbed oxygen are changed to confirm the increase in the heat recovery ratio between the feed air and the effluent nitrogen, and between the feed air and the desorbed oxygen.

During heat exchange with the heat storage material, the relationship is assessed between a) the desorption pressure and b) cycle time on the one hand, and 1) the electric power consumption rate of the rotatory equipment and heater and 2) the oxygen production rate on the other.

Based on these results, HTPSA-O₂ in this study was compared with conventional processes such as PSA-O₂ and VPSA-O₂. 

The overall results of this study are summarized as follows:

1. As the adsorption amount of oxygen on LSCF1991 shows a strong Langmuir-type adsorption isotherm, the lowest electric power consumption rate of the oxygen production and the greatest oxygen production rate versus the unit adsorbent weight are shown at a relatively low level of vacuum pressure (1-5kPa)

2. To maintain the practical oxygen production rate versus the unit adsorbent weight, the adsorption temperature needs to be higher than 500 degrees Celsius.

3. The heat recovery ratio was improved dramatically with the two cycles in different directions.

   While the heat exchange ratio of the shell & tube heat exchanger mechanism is about 80%, and that of the plate fin type heat exchanger mechanism is about 92%, the heat exchanger in the two-cycle operation mode 2 showed 95%. 

   In conclusion, the pilot unit in this study showed achievement of a heat recovery ratio for HTPSA of greater than 95% at (5m³N / h). At a rapid cycle of 100 seconds (40 seconds of adsorption, 40 seconds of desorption and 20 seconds of other operations), the electric power consumption rate was 1.46kWh / m³N, and the product amount of oxygen/adsorbent weight ratio was measured at 30m³N-O₂/h/ton (per 500kg/tower, in a 2-tower system).

   As the performance of larger scale units such as 1,000m³N/h-O₂ can be predicted from the results of this study, the electric power consumption rate is assumed to be 0.2kWh/m³N, while the product amount of oxygen/adsorbent weight ratio is assumed 30m³N-O₂/h/ton. 

   Compared with cryogenic separation, which exhibits the smallest value of 0.32kWh/m³N at the present time, HTPSA-O₂(as in this study) indicates a much lower electric power consumption rate in the future.

   It is assumed that the initial cost of HTPSA-O₂ is as expensive as VPSA-O₂ with nitrogen adsorbent.