Philadelphia-based Preferred Sands LLC, a company that specializes in proppant and flow technology for fracking wells, plans to nearly double its Houston footprint and staff within a year. Preferred Sands opened a 6,000-square-foot lab in Houston in 2013, which currently has nine employees. The lab is designed to test out new well technologies that can make fracking wells cleaner and more productive. Over the next year, the fracking tech company, which is not currently working with any specific…