The fluid is highly viscous (6,000-7,000 centipoise at 70F) and the flow is low (0.55 gpm).  The fluid is 10% NaOH and 90% wetted cellulose in water and has a specific gravity of 1.12.  I am not sure of the chance of the fluid hardening in the line and clogging the relief valve but am concerned this is a possibility.
Your material sounds like a form of paper stock, which will plug in dead legs, eg; relief valve nozzles and underneath rupture disks as well. 
You did not mention if the application used was protecting "Code Vessels", but IF NOT you may want to consider a PSH (Pressure Switch High) to "trip" the energy source eliminating the overpressure.  This scenario is used quite often in paper processes.
Agreed with psafety as the PSV will also be clogged as the fluid that you handle is very viscous. Just wanna add few discussion here, you still can comply with API RP 14C and ASME by installing the HIPPS (High Integrity Pressure Protection System) into your system, which will replace your entire PSV. You can find alots of literature about the HIPPS avail in the net.

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