"Spew" has strong connotations of a forcible ejection, so if the smoke is "billowing," then "spew" is not the best choice.
"Spew" also brings up an image of forcible ejection through an opening -- the mouth, or a volcano's topmost hole, a tailpipe, etc. So it the smoke is arising from a large area (such as a forest fire), then "spew" would not be the best word.
"Suddenly a window shattered and dense smoke spewed into the sky."
"The forest fire sent huge clouds of dense smoke billowing into the sky."
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