On the contrary, most amount of in-house recycled steel scrap is discharged from the forging process. Consequently, in-house recycled steel scrap is used rather more for cast steel parts than for forged steel parts. Because of the imbalance of recycled scrap, it seems that the authors' result for cast steel parts became smaller and that for forged one became larger.
Thirdly, there is a problem concerned with allocation. It is difficult to have meaningful statistics of the product weight, since products are manufactured in various ways and forms, and the proportion of their content fluctuates considerably according to the situation of the received orders. Since the authors allocated the total product weight to cast steel parts, forged steel parts and other products, they have to admit some errors in no small quantities in the results.
Apart from the above, it seems to be very important to acquire reliable inventory data, especially of steel crude in order to calculate the inventory data of cast/forged steel parts successfully.
4 LIFE CYCLE INVENTORY ANALYSIS OF A MARINE MAIN ENGINE
The authors made LCI analysis of the model engine discussed in Section 2.4 by using the inventory data of cast/forged steel parts calculated in Chapter 3. The results are explained below.
4.1 Manufacturing process flows
Main manufacturing process flows of a marine main engine were organized for the LCI analysis as shown in Figure 6.
Addition to the three main processes, welding process was taken into account since a considerable amount of gas was consumed.
4.2 Estimate of inventories of a unit of the model engine
The items of which data were obtained for the LCI analysis of a unit of the model are listed as follows.
(I) Input items
(Materials and parts): Cast steel parts, forged steel parts, steel plate, others (purchased equipments and other parts)
(Other materials): argon gas, CO2 gas
(Energies): electric power, fuel oil A
(II) Output items
(Products): model engine
(Recycled resources): outside recycled steel scrap
(Wastes): solid wastes (waste oil and paper wastes)
Argon and CO2 gas were taken into account as the other materials since they were consumed in considerable quantities in the welding process. The amounts of other materials such as cutting oil (machining), water, system oil and cylinder oil (land trial) and gasoline (transferring) were recorded in the factory. But they were not taken into account because they were consumed in small quantities.
In regard to electric power, the quantity used in each process was calculated by allocating the total amount in Figure 2 proportional to capacity of machines and operating time. The recorded data of electric power included the amount for illumination, ventilation and operation of tools in each building.
All fuel oil A was consumed only in the land trial process. In the factory, steel scrap discharged in the manufacturing processes was not recycled in-house but disposed outside.
The wastes which were discharged in relative large quantities and quantitatively managed in the factory, that is, paper wastes and waste oil were taken into account as solid wastes. Paper wastes were discharged mainly in unwrapping, and waste oil were mainly in the land trial and the assembling process.
In order to add CO2 emission to the waste items, it was assumed that CO2 emission is derived from combustion gas of fuel oil A and from all the CO2 used in welding process. Carbon concentration in the fuel oil A was assumed 0.848 (kg-C/kg fuel) on the basis of the IPCC Draft Guideline for National Greenhouse Gas Inventories [4].
Analysis method
Inventory data of a unit of the model engine were calculated by using the matrix-method with a 13 × 13 process matrix. Column vectors were selected as shown in Table 4. Environmental load items were calculated as same as the case of cast/forged steel parts.
Inventory data for production of energies, materials and parts were quoted as follows.
(1) Electric power: The LCA Support Database by NEC was quoted [5]. The inventory data are composed of hydraulic power generation (11 (%)), coal-fired thermal power generation (11 (%)), oil-fired thermal power generation (28 (%)), LNG-fired thermal power generation (22 (%)) and nuclear power generation (28 (%)).
