Slow-Simmered Jambalaya

2 cups diced boiled ham

2 medium onions, coarsely chopped

1 medium green bell pepper, diced

2 stalks celery, sliced

1 cup uncooked long-grain converted rice

2 tablespoons vegetable oil

2 tablespoons ketchup

3 cloves garlic, minced

1/2 teaspoon dried thyme

1/2 teaspoon black pepper

1/8 teaspoon ground cloves

1 pound fresh or frozen uncooked shrimp, peeled and deveined