1. In a 4- to 5-quart slow cooker place celery, carrots, apple, onion, and garlic. Stir in 1 1/2 teaspoons curry powder, the ginger, coriander, cumin, cardamom, turmeric, and cayenne pepper. Pour broth and the water over all in cooker.
2. Cover and cook on low-heat setting for 4 hours.
3. In a resealable plastic bag place chicken, flour, and 1 1/2 teaspoons curry powder; seal bag and shake to coat chicken with the flour mixture. Chill in refrigerator until needed.
4. In a large skillet brown coated chicken in hot oil over medium heat, stirring often. Add three to four ladles of the cooking liquid from the slow cooker to the skillet; stir until thickened and gravylike, scraping bottom of skillet to incorporate flour and spices. Stir chicken mixture and rice into the slow cooker. Cover and cook 1 hour more on low-heat setting. Stir in coconut milk before serving. If desired, sprinkle with crushed red pepper.