Bring the reserved shrimp shells and seafood stock to a boil in a large pot. Reduce the heat to medium low and simmer, uncovered, 20 minutes, stirring and skimming the surface occasionally. Strain the broth into a large bowl, pressing on the solids with the back of a spoon to release as much liquid as possible. Return the broth to the pot and keep warm.
Meanwhile, heat the olive oil in a heavy skillet over medium-high heat. Add the onion and cook until translucent, about 5 minutes. Add the carrot, celery and bell pepper and cook until softened, about 7 minutes. Stir in the tomato and chiles de arbol and cook 5 more minutes. Stir in the tomato paste and dried shrimp powder and cook 3 minutes.
Add the cooked vegetables to the broth. Cook over medium-low heat, covered, 1 hour, 30 minutes. Add the shrimp. Turn off the heat and let stand 3 minutes, or until the shrimp are cooked through. Serve with lime wedges.