Filter and environmental technologies group Porvair said it had started the year well and expects to report interim profits well ahead of 2010.Revenue growth in the first six months of the financial year is expected to be 6% at constant currency rates, the group said in a company update. Order books have strengthened throughout the period and the pipeline of potential projects is encouraging, it added.Cash generation has continued to be healthy and net debt is expected to be around £9m down from £14.3m in 2010.CJ