We are searching for a suitable Non Return Value (NRV) or any alternate arrangement which improves working life of cooling circuit NRV in slag granulation plant.
Slag granulation plant granulates molten Blast Furnace (BF) slag into a sandy non crystalline structure material which is then used in cement and construction industries. Due to rapid cooling and the impact of water pressure, molten BF slag is granulated into vitreous sand like particles which form a slurry mixture with water. This slurry mixture of water gets pumped into cooling circuit where NRVs (Non-Return Valve) are used to resist return flow and allows the pump to start in no load condition. NRVs used to fail due to abrasion caused by the slurry mixed water and hence, affects the operation of pumps. We are searching for a suitable NRV or any alternate arrangement which improves working life of NRV.
Present Slag Granulation plant has a peak capacity of 8 tonnes/minute. This system comprises of hot well tank, cooling tower, pumps, pipe lines and valves. Two water circuits, each having three centrifugal pumps operate in parallel to provide the required water for slag granulation.
A dashpot (“mechanical device for resisting motion via viscous friction) type NRV (Non return valve) is mounted after each pump (1440 m3/hr). NRV resists return flow and allows the pump to start in no load condition. Any leakage or failure in one of the NRVs affects the operation of all pumps. Life of NRV is about 6 months.
The main cause for chronic failure of NRV is due to abrasion caused by the slurry mixed water. Major components like body, disc, seat & shaft gets damaged due to abrasion and is not possible to repair. The shaft material of NRV is AISI 420 with hardness 262 HV and body material is plain carbon steel with hardness 195 HV. With an expected average life of 6 months, the current practice is to follow the time-based maintenance where we replace NRVs two times a year. In total, 24 NRVs are consumed in a year.
Low MTBF of NRV reduces the availability of RASA and granulated slag quality. The problem with low working life of NRV is prevalent in our Blast Furnace since the inception of the plant.
Options Tried Before to solve the problem: