<prompt> Translate the following text to EnglishHii ni mbinu ambayo ilichukuliwa katika ukarabati wa PSNH Merrimack Unit 2, ukarabati wa kwanza wa boiler ya makaa ya mawe nchini Marekani.  <response>: This is the approach that was taken on the retrofit of PSNH Merrimack Unit 2, the first retrofit of a coal-fired boiler in the United States. 