Effect of underflow diameter on the separation performance of natural gas hydrate desanding and purification under back pressure

Solid fluidization is a promising method for the development of marine hydrate resources. The back pressure makes it difficult to backfill the separated sand to the well bottom, resulting in a decrease in separation performance and serious failure of hydrocyclone. This study is intended to study the effect of underflow diameter on the performance of the hydrocyclone by computational fluid dynamics method. The results show that with the increase of back pressure, the split ratio basically decreases linearly, and the LAVV gradually increases. Under the same back pressure, the underflow diameter is larger, the pressure drop is smaller. No matter how large the underflow diameter is, the hydrocyclone may fail once back pressure exceeds 60 kPa. Under the same back pressure, the larger the underflow diameter is, the higher the desanding efficiency is, while the purification efficiency is opposite. When back pressure exceeds 60 kPa, the desanding efficiency drops sharply, while the purification efficiency remains basically unchanged. This study is applicable to downhole in-situ separation for solid fluidization of marine hydrate. The purpose of this study is to guide the structure design of hydrocyclone and the optimization of hydrate production process parameters.