Evaluation of Pilot Plant for High Temperature PSA-Oxygen Process Using Perovskite-Type Oxide Adsorbent
Tomoya Fujimine, Tokyo Gas Co.
Kiyofumi Monma, Tokyo Gas Co.
Jun Izumi, ADSOTECH, Ltd.
Norio Miura, Kyushu University
In this study, we constructed a pilot plant for high-temperature PSA (HTPSA) oxygen production process having a production capacity of 5 m3N-O2/h by using perovskite-type oxide of La0.1Sr0.9Co0.9Fe0.1O3 (LSCF1991) as an oxygen sorbent. At high operational temperatures of 500-800 degree C for HTPSA-O2, 1) the heating method for the adsorption tower, 2) the temperature control process, and 3) the selection of optimum operation temperature were examined in order to achieve reduction of electric power consumption rate by means of heat recovery technique. As a result, the rather lower electric power consumption rate of 1.5 kWh/m3N-O2 was estimated in this case.
Furthermore, in order to reduce the material cost of sorbent while increasing its oxygen adsorption ability, various perovskite oxides other than LSCF1991 were examined as a candidate of new oxygen sorbent. Among the oxides examined, we found that the Sr-Co-Fe-based perovskite oxide (SCF) that does not include expensive La element gave superior oxygen sorption behavior compared with LSCF1991.
To achieve a higher heat recovery ratio, the front and rear parts of the adsorption tower are filled with the heat storage material. 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 shortage of heat content is compensated for by 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 air 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 switched to assure 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, 1) the electric power consumption rate of the rotatory equipment and heater and 2) the oxygen production rate are assessed on the parameter of a) the desorption pressure and b) cycle time.
As for a new oxygen sorbent, we examined the optimum composition of SCF with regard to oxygen sorption ability. As a result, it was found that SrCo0.75Fe0.25O3 gave the largest amount of sorbed oxygen. Its amount of dynamic oxygen sorption was about 2.5 times greater than that of LSCF1991 in the evaluation by using a very small scale PSA apparatus. The performance of larger scale plant (such as 1,000 m3N/h-O2) charged with this new oxygen sorbent of SrCo0.75Fe0.25O3 can be predicted in this study.
In the near future, we will mass-produce the new SCF oxygen sorbent for a pilot plant (the sorbent usage is 250 kg) and a prototype testing plant (the sorbent usage is 4 t). Then, the oxygen production ability and the electric power consumption rate of each plant will be evaluated.
Compared to conventional cryogenic separation process which gives the electric power consumption rate of 0.32 kWh/m3N under the best condition, the present HTPSA-O2 process using perovskite oxide sorbent would be capable of showing a much lower electric power consumption rate in the future.