TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The system (S1) comprises: a fuel slurry injector configured to receive and inject the fuel slurry into the gasifier; a fuel slurry pump configured to pump the fuel slurry along a slurry flow path having the first cross-flow filter, where the first cross-flow filter is disposed in a slurry flow path downstream from the fuel slurry pump; an agitation system coupled to the first cross-flow filter, where the agitation system comprises an agitator configured to agitate the first cross-flow filter; a heating system coupled to the first cross-flow filter, where the heating system comprises at least one heater configured to heat the first cross-flow filter; a control system configured to control removal of the liquid via the first cross-flow filter to adjust a concentration of the solid fuel in the fuel slurry; and a second cross-flow filter configured to remove at least a second portion of the liquid from the fuel slurry. In the system (S1): the first and second cross-flow filters are disposed in parallel along first and second slurry flow paths, respectively, or the first and second cross-flow filters are disposed in series along a slurry flow path; the first cross-flow filter comprises many slurry flow paths extending through an enclosure, where each slurry flow path is surrounded by a filter medium; and the first cross-flow filter comprises a slurry flow path extending through an enclosure, where the slurry flow path is surrounded by a filter medium, and the filter medium converges in a downstream direction along the slurry flow path. The system (S2) comprises the cross-flow filter, and the gasifier. The slurry concentration controller is configured to control: agitation system to agitate the cross-flow filter; and a heating system to heat the cross-flow filter. Preferred Method: The step of controlling the concentration comprises controlling agitation of the cross-flow filter, and controlling heating of the cross-flow filter.