The phrase 'almost twice as many' is correct and usable in written English. You can use it when comparing two numerical values, similar to the example below: I had almost twice as many participants this year than last year at my conference.
That is almost twice as many as in 1976.
Thirty-five homesoldld in that range, almost twice as many as last year.
Half of American households now own mutual funds, almost twice as many as in 1992.
That is almost twice as many as died in the first world war.
Last year almost 400,000 people were displaced, almost twice as many as in 2014.
At full strength, it has 28 judges, almost twice as many as the next biggest circuit.
"Look at Pedro Martinez -- he's hit 11 men this year, almost twice as many as Roger.
Ludwig does not simply clarify my doubts with English writing, it enlightens my writing with new possibilities
Simone Ivan Conte
Software Engineer at Adobe, UK