Grace's Guide is the leading source of historical information on industry and manufacturing in Britain. This web publication contains 148,103 pages of information and 233,633 images on early companies, their products and the people who designed and built them.
of Maindy, Cardiff
One of a number of makers of 'patent fuel', or 'preserved coal' - a mixture usually comprising small coal - preferable steam coal - mixed with coal tar pitch and compressed into blocks, generally believed to have first been made near St Etienne (France) in 1842.
The Star works was founded in 1874 by Thomas Edward Heath and his partner Tom Evens, and located on the site of the former Maindy ironworks of Isaac Russell. An interesting feature was the use of a former GWR broad gauge locomotive, 'Nelson' of 1853, to power machinery. Heath introduced a number of improvements which faciliated production and material handling. Blocks were of regular shape and were neatly stacked on the company's wharf ready for shipping by barge on the Glamorganshire Canal to Bute Dock
The above information is taken from 'The Glamorganshire and Aberdare Canals'. This source includes photos and maps showing the Star and other works (Cambrian, Anchor, and Crown).
Further information is available on the Industrial Railway Record website. We learn that demand fell dramatically after WW1, and the works closed in December 1927. Part of the site was taken over by a furniture factory, while the north end was acquired by the adjoining Powell Duffryn wagon works. 
Another interesting source includes a 1913 advert which provides information about the benefits of Heath's patent dry heat process, and of the convenience of stacking and stowing the blocks, with 1 ton of blocks occupying only about 32 cu ft, compared with about 42 for large steam coal. The average weight of the blocks was 23 lb (10.5 kg).