A fuel slurry heating system includes a fuel slurry preparation system which comprises a fuel slurry vessel configured to hold the fuel slurry, a heat source and a controller configured to control the heat source to heat the fuel slurry to decrease a viscosity of the slurry below a threshold viscosity to make the slurry pumpable, and the fuel slurry is composed of a solid fuel and a liquid. And a corresponding method for using the heating system to heat a slurry to increase a solids concentration of the slurry while maintaining the viscosity of the slurry below a threshold viscosity is also disclosed.