Cash flows across the energy sector tend to be more variable due to commodity price volatility. However, some energy stocks just print money because their business models have minimal direct exposure to commodity prices. That gives them the cash to pay lucrative dividends. Energy Transfer (ET -0.42%), Kinder Morgan (KMI 1.58%), and Williams (WMB 2.27%) operate money-printing energy midstream assets. Because of that, they're ideal options for investors seeking to generate passive income. Revving up the money ...