Phosphine generator trial using external air dilution

Abstract

A commercial phosphine (PH₃) generator manufactured by Beijing Liangmao Technology Development Company Limited, China was used in a fumigation trial on 5000 tonne bunker storage. The generator’s production of PH₃ is controlled by the rate of dosing conventional aluminum phosphide (AlP) tablets into 100 kg water in the reaction chamber.

Because PH₃ is flammable and explosive if certain a concentration is reached in air, it is usually mixed with carbon dioxide (CO₂) in the weight ratio of 50:1. This trial’s objective was to minimise the amount of CO₂ and dilute the generated PH₃ with air. The PH₃ generated is purged from the reaction chamber by a continuous low flow of regulated CO₂ gas. The PH₃-rich CO₂ purge stream was fed into the suction inlet of an external venturi. A high pressure fan was used to produce the air flow through the venturi to create the vacuum to suck in and dilute the PH₃ rich stream from the generator. The PH₃ was diluted in the air-flow to ensure a non-flammable concentration of less than 1% (10.000 ppm) and thence fed directly into the bunker storage. The trial successfully demonstrated the viability of generating phosphine in this manner, and excellent results in PH₃ concentration and distribution was achieved in very short time periods. The capacity of the generator was limited to 8 kg of AlP tablets, equivalent to 2.667 kg of PH₃, or sufficient to fumigate 2667 m³ of grain at a dosage rate of 1 g/m³. A much larger version of the machine would be required to fumigate medium size bunker storages in the 10.000 to 15.000 tonne range. Notwithstanding, the generator offers an attractive package combining the speed and convenience associated with the use of gaseous PH₃ with the low cost of AlP formulations.

Keywords: Phosphine fumigant, On-site generator, Metallic phosphide, Non-flammable