Capacitor commutation of thyristor and DC load
ON Semiconductor's Thyristor Theory and Design Considerations Handbook should give you some interesting bedtime reading.

Section 5, page 60, starts:


  SCR TURN−OFF TIME \$ t_q \$
  
  Once the anode current in the SCR ceases, a period of
  time must elapse before the SCR can again block a
  forward voltage. This period is the SCR’s turn−off time,
  tq, and is dependent on temperature, forward current, and
  other parameters. 


The information you require is, I think, on page 128.


  $$ C_c = \frac {T_q I_A}{V_c} $$
  Where:
  
  
  \$ C_c \$ = value of necessary commutating capacitance
  \$ T_q \$ = turn-off time of the SCR
  \$ I_A \$ = value of anode current before commutation
  \$ V_c \$ = voltage of Cc before commutation
  
  
  This relationship shows that to reduce the size of \$ C_c \$, the
  capacitor should be charged to as high a voltage as possible
  and the SCR should be selected with as low a turn-off time
  as possible.


The article goes on to give calculations for a motor control application.

I am unable to find any \$ T_q \$ specifications for your thyristor.