Put the rice with the salt in 3 cups of water in a medium saucepan. Bring it to a boil, reduce the heat, cover, and simmer until the rice is tender and the water is absorbed, about 45 minutes.
Trim the tough ends off the asparagus stalks and discard. Steam the asparagus until tender yet crisp, about 2 minutes. Drain it in a colander, then rinse under cold water. Let the asparagus cool for a few minutes. When completely cooled, cut into 1-inch pieces, reserving 1/4 cup of tips for garnish.
Coat the bottom of a large pot with the olive oil. Add the celery, onion, carrot and thyme. Cover and cook over low heat for 4 minutes, stirring occasionally, until tender. Add the vegetable stock and cooked rice and bring to a boil. Reduce the heat, cover, and simmer for 10 minutes. Remove from the heat and let cool a bit.
Carefully transfer small batches to a blender and blend until smooth. Return all the blended mixture to a pot. Stir in the asparagus, scallions, parsley, soy sauce, pepper sauce and ground pepper. Return to a simmer for 2 minutes. Ladle into bowls and garnish with reserved asparagus tips and parsley sprigs.