Season shrimp with Creole seasoning and curry powder. Set aside.
To a Dutch oven or stock pot set over high heat add 2 quarts water, reserved heads and shells, onion, pepper and celery trimmings and 1 teaspoon salt and 2 quarts water. Boil vigorously for 20 minutes, skimming foam as it cooks. Remove from heat. Drain to remove solids, reserving liquid. Two cups of stock will be used for the recipe. Reserve the rest for later use. Set aside.
Melt butter on medium high in a 6 quart Dutch oven. Add diced onion, celery, and bell pepper with 1 teaspoon salt and cook until soft, about 20 minutes. Add the flour and stir until pasty, 1 to 2 minutes. Add coconut milk and cook until slightly thickened, about 5 minutes. Add the drained, mashed sweet potatoes and stir to combine. Using an immersion blender, blend until uniform and fairly smooth. Add 1 cup of the reserved shrimp stock, and stir until slightly thinned. Add the zest of half a lime and the juice of both limes. Add the bay leaves, ginger, nutmeg, pepper flakes, cayenne and white pepper and blend. Add the shrimp, reduce heat to medium-low and simmer for 5 to 7 minutes or until the shrimp are just pink. If thinner soup is desired, add more stock, 1/2 cup at a time, until desired consistency is achieved.
Serve garnished with green onion and lime wedges.