General of stone crusher
The crushed stone industry in developed country like USA is the largest non-fuel, non-metallic mineral industry with respect to both total volume and value of production with about 901 million tons production valued at over 2 billion US $ in year 1975. The industry is geographically highly dispersed with all states. The stone production by individual states is proportional to population and industrial activity. There are over 5400 crushers in the USA located in urban, suburban and rural areas.
Plans are either stationary or portable type in the capacity range varying from 100 tons to several thousand tons per hr. The various rock type processed are lime stone, granite, trap rock and sandstone. Important products include construction related material such as specified and unspecified construction aggregates and road stone, concrete aggregate, bituminous aggregate etc. As per USEPA data, the crushed stone industry was ranked third highest among the nations 56 no. of largest particulate source emitting category industries in the year 1975.
The above table shows that out of the total 5214 quarries, about 39% are small scale quarries which contribute only 1.6% of total production, on the other hand the large quarries are only 3.2% in number but contribute 31% of total production. Typically a large number of small, locally owned farms account for a minor proportion of national production whereas a small number of larger firms which are regionally or nationally diversified account for a large percentage of overall production.
Stone crusher prices
The prices of the crushed stone in USA vary from place to place depending on the transportation involved, costs of raw material, size of crushed stone etc. Typically the prices range (converted in equivalent Rs.) from Rs.90 to Rs.370/ton for 1.5″ size stones and about Rs.250/- per ton for 0.75″ size stones. Typically the transportation costs range from Rs.25/- to Rs.75/- per ton from the quarry to city.
The financial profile of typical stone crusher plants indicates the industry sector operates on an average profitability of about 7%, the industry if capital intensive, depreciation and depletion represent major sources of funds for capital expansion and a major portion of the industry’s assets is tied up in working capital, primarily inventories and accounts receivable.
Crushed stone is generally distributed directly from the quarry to the user with no intermediary involved. It is readily available in most metropolitan areas because transportation and distribution are predominantly by truck. Inventories are held almost entirely at the quarry location because double handling would be prohibitively expensive, and customers maintain only sufficient inventory to ensure uniform production rates over a pre-determined time. Typically the crushers operate for 9 months in a year in USA.
As per USEPA estimates, a typical crusher process (excluding quarry and other fugitive dust sources) may emit up to 5.5 kg. of dust per ton of crushed stone produced equivalent to 0.55 %. In the absence of any air pollution controls, the particulate emissions from the crusher industry countrywide were estimated to have exceeded 4.9 million tons during 1975.
Typical emission factors from various sources
The above table indicates that maximum emissions occur during tertiary crushing and screening operations, followed by re-crushing, material handling and conveying followed by secondary crushing and screening and primary crushing.
In the washing section, sometimes to meet specifications of some aggregate products such as concrete aggregates require washing to remove fines. Because it is wet process, it essentially produces no particulate emissions.
In USA, several processing units are portable plants consisting of a single chassis on which all the crushing equipments are mounted. Emissions from each processing unit in a portable plant are the same as those from a unit of equivalent size in a stationary plant.