问下,as……as……结构中as为什么词性?conj么?“像……一样”,

问下,as……as……结构中as为什么词性?conj么?“像……一样”,
Although they've been there before,they still feel as excited as if it were their first time.
另外问下,这里如果把第一个as去掉,没语法错误吧（我知道意思有点变.）