Oleg G. Vorobyev, Andrey V. Shamshin

St. Petersburg State Marine Technical University

A geotechnical system is an open system in which an industrial object (enterprise, industrial plant or complex) exchanges mass and energy with a surrounding environment. Such systems can be described by equations which are not susceptible to analytical solution and consequently a more productive approach is based on systems analysis and simulated mathematical modelling. The construction of models with wide predictive possibilities allows us to reduce to a minimum the use o statistical methods which, in conditions where the processes under study are undergoing rapid changes, are insufficiently reliable. We try to construct that model with help of system and exergy analysis.

The modern period has been marked by sharply increased ecological tensions, both globally and in specific regions where the issues are particularly acute. The negative consequences of human activity continue to generate ecological problems, reflected in a growing wave of demands for the adoption of prompt remedial measures. Unfortunately, such calls frequently do no more than reiterate the necessity for environmental protection and lead at best to isolated and partial successes, most typically in blocking the construction of some environmentally damaging enterprise. It is substantially more difficult to tackle problems associated with already established enterprises, especially if they are obviously profitable. In most such cases economic priorities prevail even if ecological damage results. Nuclear power stations and pulp-paper plants are well-known examples, as are the great majority of ferrous and non-ferrous metallurgical, chemical and petro-chemical plants. And in all cases the roots of the problem can be traced to a lack of ecological awareness in the planning of industrial projects. There is inadequate appreciation or even total ignorance of the fact that an industrial plant itself constitutes a unique pro- and reactive factor, transforming the substance of nature, generating mass-energy fields and producing local ecological stresses capable of developing into regional and in extreme cases even global tensions.

The time has come for us to move from the planning of discrete industrial enterprises to the planning of geotechnic systems (GTS) with adequate prognoses of the situations which may in practice arise through the interplay of technogenic and natural factors. This is the concern of ecological engineering, which can claim recognition as an independent branch of science, dedicated to providing a methodology for ecologico-economic assessment and management of the interaction between industry and the environment and to developing concrete means and practical approaches to the rational utilization of natural resources on the basis of scientifically established regional ecological limitations.

Analysis of the current ecological situation shows that we are dealing, not with isolated errors in the technology of resource extraction and processing, but with a fundamental discordance between contemporary technological processes and those of nature. The policy of intensification of production by simply increasing the size of plants and crudely boosting their productivity can make no further headway, though such a course still obtains in association with the solidly rooted inertia of development policies in ecologically irresponsible regimes. Measures introduced for the improvement of purification systems and other cleansing techniques as an artificial filter between production and nature are also no solution, because the level of purification of waste products which is economically justifiable is inadequate to prevent environmental pollution; rather such measures merely delay its consequences for a time. This is especially noticeable when we calculate the more long-term results of resource depletion and environmental pollution, manifested in a critical increase in expenditure on conditioning of raw materials, water and air, an outlay directly resulting from current human activity.

The need for a root-and-branch review of the principles of resource use was recognised some time ago, marking a move toward a third stage in the relationship between nature and human beings. In principle there are two ways to fight environmental pollution; either purification of dangerous waste products or the development of technological processes which imitate natural processes as far as possible. The absence of an accurate estimate of the economic damage caused by pollution serves to obscure the economic advantages of this second policy. Whatever the economic benefit in liquidating such damage, it would, as a rule, have been less costly to prevent its occurrence; that is, the move to an ecologically sensitive technology is not only dictated by the need to defend the environment but is economically expedient.

It must be recognised that, in mobilising technological advances in the cause of environmental conservation, we cannot simply copy natural processes, because humanity has already created materials which do not exist in nature (Preobragenski 1978). This means that the "ecotechnology" of the future will not be based on complete replication of natural processes; these latter are, in any case, far from exempt from producing wastes, though always equipped with components for recycling or destruction (decomposers in trophic chains). At the same time one should reckon that more intensive processing of by-products, with an increase in the number of fractions containing components in tiny concentrations, can lead to an increase in the quantity and variety of waste products and is associated with a need to use significant quantities of energy and auxiliary materials.

In the real world the development of society, as of nature, is a process that cannot be reversed, and it is therefore false to suggest that we can eliminate the ill-effects of actions which disturbed some previously existing equilibrium state. More feasible is a policy aimed at utilising scientific and technical progress to establish an optimal relationship between society and nature, achieved through the combination of superior technology with a high degree of environmental awareness, as envisaged by V. Vernadsky. One should add that it is not enough just to lay down the principles of a technology of minimal waste production. Any industrial complex must be located and planned with an awareness of general and regional natural, and specifically climatic conditions, in such a way as to minimise impact on the environment, particularly on its mobile or circulating components - the hydrosphere and atmosphere.

No transformation of nature should be undertaken without due regard for its social, economic and ecological consequences. This is possible on the basis of socio-economic models, where the ultimate aim is to optimise both economic outcomes and environmental relationships within the constraints imposed by ecological, socio-economic and technological potential. Given a particular level of development of productive potential, the pattern of utilisation of natural resources with the strongest theoretical basis is that which, while delivering the highest economic yield, also avoids environmental degradation. This demands a special location policy for production facilities and their spatial organisation on a very large scale, opening up possibilities afforded by scientific advances, notably in chemistry, to draw into secondary utilisation significant amounts of accumulated waste material. In Russia the need to integrate

on a regional level all the links in the production chain, attached as they were to various decision-making bodies with different corporate responsibilities, inspired the pursuit of a new spatial organisation of production facilities and the formation of territorial production complexes or TPCs. Such a policy gives priority to the interests of the regional economy as a whole and not to those of separate branches of industry.

The development profile of any individual TPC and its economic specialisation is largely conditioned by the resource potential of the regional environment, which in turn depends not only on its range of components but also on the state of the system they compose and the

dynamics of their changes. The organisational-technical structure of the TPC is based on the concept of production-technological cycles. Analysis of TPC structure and the exchange of mass-energy and information flows between its productive elements and the natural environment can be usefully undertaken adopting the notion of resource cycles elaborated by I. Komar. Consequently, at all hierarchical levels of the interaction between industry and the environment, from the level of the single industrial plant to that of the TPC as a whole, we observe mutually exchanging matter, energy and information flows which fuse the technical and natural systems into a single geotechnical system (Komar 1976).

Fig. 1 depicts a geotechnic system formed through the establishment of an undustrial enterprise. The plant draws into its sphere of production raw materials and other natural resources and emits into the environment byproducts of its technical processes.

Natural and man-made flows of matter and energy bring about the redistribution of these waste products through processes of migration, transformation and accumulation.

Thus dust and gaseous emissions from facilities storing liquid or solid wastes create atmospheric pollution. Rainfall, flushing pollutant substances from the air, transfers them to the land and water surfaces below, including reservoirs, and also promotes the washing out and leaching of fine-grained and soluble constituents of technogenic or natural origin and their migration within surface or sub-surface waters. Further, there is mutual quantitative and qualitative exchange between surface water and groundwater.

An environment subjected to technogenic pollution displays negative effects on plant and animal life. However, the nature of the reactions of the biota to pollution is a topic for separate study, beyond the compass of this book. Here we shall limit ourselves to examination of the abiotic environment subjected to inputs of waste products from an industrial plant.

Examining the schematised structure of the GTS as a particular type of environment-technogenic complex, we note that the natural elements (water, air, soil, minerals etc.) function not only as environmental components but as resources exploited for production. The intensity of mass-energy transfers within the GTS is governed primarily by the nature of the technical processes. The chemical industry in particular is characterised by profound, sometimes total transformation of both its basic raw materials and its auxiliary materials, with alteration of their properties and the formation of byproducts.

The industrial plant (IP) and its surrounding environment (SE) form the system IP-SE. The integrated set of variables within the system can be generalised in the form of a law of internal equilibrium; the system possesses internal energy, matter, information and dynamic qualities interconnected to such an extent that any change in any one of them calls forth changes in another, change of equal magnitude but carrying, mathematically, a minus sign and thus conserving the overall sum of mass-energy, information and dynamic properties in the system.

The balanced equation for the system at the black box level takes the form:

, (1)

where M_R represents raw material inputs from within and beyond the GTS, M_P is primary resources (water, air) drawn locally for auxiliary purposes, M_W is the outflow of waste products (net, i.e. excluding wastes drawn back into production) and M_PR is finished product.

`Fig. 2. moves to grey box level, where the system blocks are Production (1), Surface Waters (2), Groundwaters (3), Lithosphere (4) and Atmosphere (5). In the system interpretation, every block has a definite volume, containng specific pollutants (not counting the carrier - water, air etc) conditionally classified as toxic in relation to the natural environment.

To simplify the model we examine only the flows of matter within the system, leaving aside flows of energy. Such a simplification is permissible in the first stage of analysis of the environmental impact of an industrial project.

Returning to equation 1, we should note that the quantities entering into it define the store of toxic chemical compounds interacting with the surrounding natural environment under the influence of various natural and technogenic factors. Industrial waste products (M_W) entering the environment can be represented in the form:

, (2)

where m(A), m(S), m(G) and m(L) represent the residue of toxic components (volume of the block), formed by waste products entering, respectively, the atmosphere, surface waters, groundwaters and

the surface of the lithosphere. The final or net values are, however, determined not only by the mass of waste emissions from the enterprise but also by the subsequent interaction between the waste products themselves, consequent on processes of migration, transformation and accumulation of the toxic components of waste materials within the surrounding environment, together with return (recycling) to the plant.

Assuming that the plant (the block "Production" in Fig. 2.) is itself a subsystem containing i workshops or departments connected with the external environment by flows of waste products and primary resources, equation 2 takes the form:

To compare and analyse the balanced equations of the system at different hierarchical levels, we need first to explain the labelling of the blocks and flows and understand their nature. The "grey box" schema in Table 1 depicts flows only among the four "natural" spheres" which we have distinguished as system blocks comprising the natural environment, each flow being labelled with two index letters, the first designating the source block, the second the recipient. Table 2 itemises flows of matter connecting the enterprise - the block "Production" - with the environmental blocks (see Fig. 2.); here each flow is identified by two numbers denoting, respectively, source and recipient blocks. Designation of flows in the system at the "white box" level derives from analysis of the sequence: system - block -flow; this scheme allows us to define the essential nature of a flow of pollutants for any number of levels.

Taking into consideration all the various flows of matter, from the extraction of raw materials to the output of finished goods, one can represent the technological parameters through balanced equations of the following form:

, , (4)

where a _j is the content of useful components in the raw material, g _j is the quantity of such components actually recovered into the product, b _j is the content of such components within the product, Mpr_j is the mass of output of the e _j-containing product and Mr is the mass of raw material processed in production.

These equations make it possible to calculate technological indicators depending on the particular sequence of stages involved in the technological processes. Equation 5 defines the mass of product of j-th type produced by means of the i-th technology - including the stages of raw material extraction (RM), its crude (crushing, sorting) initial processing (IP), its enrichment or final concentration (EN) and chemical transformation (CH), and noting also the mass of by-products utilised outside the enterprise (UW) and non-utilised wastes (NW).

(5)

The mass of waste product (M_W) of m-th type created through the i-th technology, considering both utilised () and unutilised () portions and differentiated by technological process stages, is determined by the formula:

(6)

where n is the number of successive technological stages. During raw material extraction, waste of the m-th category is mainly stripped-off overburden. At the stage of initial raw material preparation (crushing etc.) such wastes are represented by barren rock, at that of enrichment they comprise residues from concentration, and at that of chemical transformation such chemical byproducts as slag, ash, sludge etc. Besides this, all technological stages generate gaseous and dust emissions and effluents, removing from the plant a portion of the raw and auxiliary materials, byproducts and even finished products, thus including them in the mass of waste products of the system. As a result of the mobility and dynamism of gaseous and dust emissions and of liquid effluent, it is this group of wastes that causes most damage to the surrounding environment.

The mass of utilised byproducts of the m-th category, mobilised in processes of the i-th technology to produce additional output of the j-th type, is determined by the formula:

, (7)

where r _ij is the "expenditure" coefficient of byproducts in the m-th category, used to produce the j-th output employing the i-th technology.

This approach can by used to reach an approximate quantitative assessment of the direct effect of an industrial plant on its external environment, but it cannot yet give a full picture of the role of supplementary exchange flows in creating the final cumulative or aggregate load on the environment. The sum of accumulated unutilised waste products is calculated by the formula:

(8)

This total reflects the uncontrolled action of the production system on its surroundings. For closer assessment of this action we need to know the dynamics of all uncontrolled production influences on the environment. If production, in a generalised form, involves the reaction:

(9)

Then the general velocity of the transformation of matter is described by the static equation:

(10)

and the uncontrolled action of wastes on the environment is obtained by the dynamic equation:

, (11)

where u is the controlled effect in production, the indices N and TE represent mass present in respectively, the natural and technogenic environments, and T is temperature. Resolution of the dynamic equation comes down to search for values q and u which provide the extremal value of the functional J = J (q,u). Here the magnitude of M is defined by reference to the efficiency of production.

To determine the uncontrolled effect we must investigate the processes of migration, accumulation and transformation of waste products within the surrounding environment and the resultant build-up of fields of concentration of the various constituents of such wastes. However, analysis of the balanced equations of natural subsystems at white box level brings together two conflicting points. On the one hand, increasing the complexity of the mathematical model by multiplying the number of flows creates insurmountable problems for solution of the system of equations describing the object of study. On the other hand, a reduction in area of the individual spatial elements of System IP-SE provides concrete practical conditions for experimental study of the exchange flows. In other words, further differentiation of exchange flows can move the solution of the system to a mathematically higher order of complexity, while, however, reducing uncertainty in experimental study of the system, using selected basic sites.

Because of the limited possibilities of systems analysis in the investigation of exchange flows on the principle of subdividing the structure of the systems of the natural spheres, quantitative methods need to be introduced. However, such an approach is only productive when coupled with an accurate systems interpretation - an adequate model - of objective reality.

1. Preobragensky, V. eds, 1978. Nature, technics, geotechnical systems. Moscow: Nauka (in Russian).
2. Komar, I.. 1976. Efficient use of natural resources and resources cycles. Moscow: Nauka (in Russian).
3. Vorobyev O. G., Shamshin A. V. and Muzalevsky A. A. 1998 Opportunities of application of the exergy method of analysis of interection between industrial object and environment. Ecological Chemistry, 7(2), pp. 110-115. (in Russian).