Here, "naphthalene refining residual liquid" refers to a liquid by-product generated and remaining from distillation, crystallization, washing or refining separation steps during the refining of naphthalene in coal tar or related feedstocks, typically containing unseparated naphthalene, other polycyclic aromatic hydrocarbons, sulfur- or nitrogen-containing organic compounds and small amounts of impurities. After such naphthalene refining residual liquid is no longer used as a product or is discarded, following collection, separation and reprocessing it can be recovered and reused as a chemical raw material, returned to the relevant processing steps, or further disposed of provided environmental protection requirements are met.