A process for pressurizing bulk material in a hopper; wherein the hopper is configured as a lock hopper (29) containing a bulk material, a source of pressurized gas, lines (22, 26, 28) to convey the pressurized gas from the source to one or more inlets (30) of the lock hopper, a valve arranged in the lines, wherein the opening position of said valve (34, 35) is controlled to provide pressurizing gas to the lock hopper at a preset constant gas volume flow rate.
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