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Cleaner Production (CP) Scheme For Stone Crushing Industry Safdar Imam safdar@sdalt.ernet.in __________________________________________________________________________________________________________ Stone crushing industry is an important industrial sector in the country, engaged in producing crushed stone, used as raw material for various construction activities, such as roads, bridges, buildings, canals etc. The construction and infrastructure sector was estimated to grow @ 8% per annum in the 9th plan period. It is estimated that, there are over 12,000 stone crushing units in India (covering small, medium and large scale).The number is expected to grow further in view of the future plans for development of country infrastructure. Stone crushing sector with an annual turnover of over Rs. 5000 crores provides direct employment to over 500,000 people. Most of these personnel, engaged in various activities (mining, crushing, transportation of mined stones and crushed products etc.) are from rural and economically backward areas, where employment opportunities are limited.And therfore, stone crushing industry carries great significance in terms of social importance. The stone crushing sector, though socio-economically important, create a substantial amount of environmental pollution by way of both process sources and fugitive sources. It is a well known fact that most of the workers engaged in stone mining, crushing, transportation etc., suffer from several occupational health hazards (severe cough, lung disorders, etc). Dust emission has visible adverse impact on environment. Agricultural land and forested area are also affected due to emissions. Keeping in view the need for worker’s health and environmental problems associated with stone crushing sector, it become necessary and important to develop Cleaner Production (CP) scheme to mitigate hazardous impact on environment and human health due to regular exposure to high dust level. Cleaner Production (CP) as defined by UNEP is the continuous application of an integrated preventive environmental strategy to processes, products, and services to increase overall efficiency, and reduced risks to humans and the environment. Apart from pollution reduction it also provides some direct benefits to the industry, such as:
A study of the production process and environmental status was conducted by Development Alternatives in four selected stone crushing units of Madhya Pradesh with financial assistance from SIDBI, Bhopal. The study was conducted through preliminary visit & survey for collecting baseline information such as, raw material, plant capacity, process details, equipment & energy consumption, crushers, screens and material handling equipments etc. In addition, dust control practices and water availability status was also collected.
Based on the results of Ambient Air Quality Monitoring (AAQM), it is found that, the dust level in ambient air is higher than prescribed CPCB norms(suspended particulate matter of a stone crushing unit shall not exceed 600 µg /m3 ). Therefore it is necessary to reduce the level of dust in the ambient air through implementation of Cleaner Production scheme i.e. dust suppression and dust containment. Unit level dust contribution in typical stone crushing units is shown graphically: In order to reduce such a high dust level in a unit, the following cleaner production options have been suggested:
i. Wet type System
For a wet type dust control system to be effective, it is necessary to provide containment enclosure for the following key locations:
- The dust suppression system comprises of providing moisture into the material flow by spraying water at key dust generating locations to restrain fine particulate matter from becoming air borne. The objective of wet dust suppression is not to fog an emission source with a fine mist to capture and remove particulates emitted, but rather to prevent their emission by keeping the material moist at all process stages. It is usually necessary to apply it at several points beginning as soon as possible after the stones are introduced into the plant. The wet type system is useful in the place where water is easily available. The cost is less as compared to dry type system and reduces dust upto 70% in the ambient air.
Keeping in view this scenario and limitations of water spray systems, a dry type control system would be suitable for such crushers to ensure a desired level of dust control. The dry type dust control system comprises of adequate Enclosure of key locations with hooding arrangement for extraction of the dust, and arrangement of Cyclone or Settling Chamber to collect the coarser portion of the dust, and a Bag-filter house to capture the finer portion of the emission not captured by Cyclone or Settling Chamber etc. The sufficient capacity of extraction and pressure drop across the system would be required to be provided by installing an induced draft fan of sufficient capacity. The details of the systems component are briefly described below:
The dry type system is suitable for the area where water scarcity is also a big problem (mostly dry region). The cost is more than the wet type system and reduces dust upto 90% in the ambient air.
As an alternative to the expensive dry type control systems in terms of capital investment as well as annual operating cost, a combination of dry and wet type control system has also been suggested. In the combination system the dust is suppressed at some points with water sprays and from some points the dust is extracted with the help of an induced draft fan and can be captured in dry type or wet spray chamber type control equipment. Such combination control systems are commonly used in stone crushers in developed countries like USA. This has benefits in terms of avoiding a coating of dust on the stone products, reduces dust upto 99% in ambient air and at the same time is less expensive than dry type control system, however it would be more expensive than wet type system.
Based on the above study in stone crushing industry, it is concluded that, the existing control measures such as, dust containment enclosures, water spray arrangements etc., are generally found to be inadequate, due to inadequate containment, inadequate water quantity, inappropriate spray locations etc. The environmental management scenario in the stone crusher sector can be substantially improved through designing and adopting customized cleaner production schemes. Adoption of such scheme would also increase the productivity of units by way of reduced dust generation, reduced energy consumption, lesser breakdowns leading to increased plant easy accessibility. |
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