精馏塔用严格法出错，求助

a41524

ASPEN模拟后出现这样的错误警告，请问要如何修改？我先是用DSTWU简捷运算，之后用RADFRAC严格法计算就出现这样的问题。

Block: RADFRAC  Model: RADFRAC

      INFORMATION

      FLASH RESULTS ARE WITHIN TOLERANCE, BUTMAY BE UNSATISFACTORY BECAUSE

      EXTRAPOLATED EOS VAPOR VOLUME ROOT WASUSED FOR PROPERTY CALCULATIONS.

      COMPOSITE FEED FLASH FAILED TO CONVERGE;COLUMN CALCULATIONS CONTINUE.

      IF CALCULATIONS FAIL, SUPPLY T-EST ANDOPTIONALLY BOTH X-EST AND Y-EST.

       Convergence iterations:

         OL  ML   IL     Err/Tol

          1   1   10      640.13

          2   1   10      220.53

          3   1    3      105.41

*** SEVERE ERROR

      THE FOLLOWING STAGES DRIED UP (VAPOR ORLIQUID FLOW APPROACHES 0):

        4  12

      A LIMIT OF  0.10000E-04 * SUM OF FEEDS WAS IMPOSED ON THEFLOW RATES

      OR A LIMIT OF  0.10000E-04 WAS IMPOSED ON THE STAGE V/L ORL/V RATIO.

      INFORMATION

      CALCULATED REBOILER DUTY IS NEGATIVE.