Hi Tony,
Thanks for posting this nice picture. Some time ago I wrote a short article for British Railways Illustrated which is attached and which gives some of their back story. As Mark has posted there were two fleets of triple silo powdered coal wagons :
Yorkshire/Durham wagons lettered 'Pulverite' and owned by the Standard Pulverised Fuel Company, dating from the mid 1930s.
South Wales wagons which were originally developed by Powell Duffryn Amalgamated Collieries in the 1940s and then subsequently passed to NCB ownership.
I have a very poor view of Pulverite 1016 at Brancepeth Colliery in 1962 so that is where they were loaded at that period. However their destination remains unknown but it would have to have been a plant equipped with discharge gear specifically built for these wagons, possibly dating from the mid 1930s when they were brought into service.
Best,
Pete