A questionnaire inquiry on prior accidents was conducted among local government operating sludge drying and incinerating facilities and cooperating research companies that are constructing such facilities. The 88 accidents reported by the respondents were investigated and the causal mechanisms associated with each typical accident pattern (by type and origin of combusted material, by accident factor, and by nature of spark) were clarified. Based on these causal factors safety measures have been indicated in an easily comprehensible manner.
1. Purpose of Study
As a result of the wider utilization of sewage sludge, accidents due to combustible sludge-derived gases have occurred more frequently. While sewage sludge constitutes a valuable fuel because of its high calorific value it does give rise to spontaneous exothermic reactions and to dust explosion risks. Its use therefore requires particular precautions.
The purpose of this study is to clarify the behavior of the combustible sewage-sludge derived gases that are apt to cause problems during sewage sludge treatment and utilization and to identify the appropriate safety measures in an attempt to promote the effective use of sewage sludge.
2. Description of the Study
(1) Studied Sludge Treatment Process
The following facilities were studied.
- Transport and storage of dehydrated sludge
- Drying, carbonization, incineration, melting of dehydrated sludge
- Transport and storage facilities for dried sludge and carbonized products
(2) Survey of prior accidents
The following precedents of accidents were reported.
- Abnormal pressure rise, explosion, abnormal exothermic reactions, spontaneous ignition
(3) Survey of risks of studied materials
Risks study was carried out on the following:
Combustible gases, carbonized products, dry sludge
(4) Causal factors of accidents
Factorial analysis was carried out on eight main accident precedents, including explosion in the incinerating equipment.