An expansion joint for a solids return system includes a female joint portion, a male joint portion received by the female joint portion, the male joint portion and the female joint portion forming a lateral breach therebetween, a double rope seal positioned within the lateral breach, the double rope seal being configured to accommodate relative lateral movement between the female joint portion and the male joint portion, and an insulating pillow received about the male joint portion and abutting a distal end surface of the female joint portion, the insulating pillow being configured to accommodate relative axial movement between the female joint portion and the male joint portion.