Бурение грунтовых зондов, установка энергетических колодцев

9.1 ECONOMICS

The economics of every major capital investment are individual to the project concerned. Given the broad range of applications and feedstocks, this is especially so for gasification. Nonetheless a number of trends can be identified.

Gasification is generally a capital-intensive technology, which has, however, the capability of working with cheaper or more difficult feedstocks than many alter­natives.

Ammonia. The capital intensity of gasification is clearly visible in the data in Table 9-1 for a 1800 t/d ammonia plant located in Northwest Europe based on different tech­nologies and feedstocks. The capital estimates and feed rates are those of Appl (1999).

This data can be presented in a manner that allows comparison of production costs with varying feedstock pricing for the different feedstocks, as in Figure 9-1. Based on these data ammonia production by gasification of heavy residue becomes competitive with U. S.$2.50/MMBTU natural gas, if the residue is valued at about U. S.$20/t. The natural gas price must rise to over U. S.$4/MMBTU before coal or petcoke can become a competitive feedstock.

Methanol. Higman made a similar study for methanol comparing natural gas and vacuum residue feed (1995). The results are in principle similar (Figure 9-2).

His conclusions are that under today’s economic conditions, it would not be competitive to manufacture methanol by gasifying locally available resid compared with importing methanol produced from cheap natural gas in a remote location. “If, however, strategic or other considerations demand that production be located in one

of the major industrial countries, then a fall in the residue price could make addi­tional capacity of this sort more attractive.”

Synfuels

The economics of gas-to-liquids (GTL) projects is dependant on both a cheap source of natural gas and the capital investment. The main incentive for such projects is to provide a means of bringing gas from remote or other locations where it has little value to the world energy market. For long-term contracts at such locations, natural gas prices of around U. S.$0.70/GJ are achievable—a very different situation from gas prices in Western Europe or North America.

The investment costs for GTL projects have dropped dramatically since the first — generation (Bintulu, Mossel Bay) projects with the introduction of “second-generation” technologies. Published data indicate specific capital expenditure of U. S.$20,000- 30,000 per installed bpd of liquid product capacity. Clearly, for a remote location, the cost development of a local infrastructure will be a major uncertainty in such numbers and will be highly project-specific.

Taking this data for a 50,000 bpd project and a conversion efficiency of 8.5 GJ/bbl, production costs work out at about U. S.$23/bbl of refined product at the remote location. Given the premium quality of the product, this is a figure that can justify such projects at current oil prices, but the margins will not be spectacular. On the other hand, the existence of such plants and the experience gained with them would be a rewarding investment should oil prices rise significantly.

Power Production. As with chemical applications, the economics of power production using gasification technology is dependant on the clean utilization of cheap feed­stocks. In many parts of the world the power industry is experiencing a period of change, brought about by privatization and deregulation, which does not make decision making easy. In a recent study conducted for the U. K. Department of Trade and Industry, it was found that even the cheapest technology, natural gas combined cycle (NGCC), is not viable at current U. K. electricity prices of around 0.02 £/kWh (-0.03 $/kWh) (Ricketts etal. 2002). However, such a situation cannot be expected to continue over a longer period of time, so there is considerable value to reviewing the factors, which can make gasification a competitive option. It must, however, be appreciated that there are two or even three markets that need to be considered sepa­rately. In the market for large utility plants, only coal and refinery residues can provide the feed volumes required. Biomass and waste are fuels that, for reasons connected with the logistics of the fuel supply, can only support small units (say <50 MW). At this scale, the cost of electricity production is higher than for utility-size plants; such projects can, however, attract financial support on the basis of environmen­tal benefits or in the case of waste by charging a gate fee. The third market where gasi­fication is showing promise is co-firing syngas from a biomass gasifier in a utility-scale plant, thus securing the benefit of scale without overloading the fuel supply logistics.

Figure 9-3 shows a typical investment cost breakdown for a coal-based IGCC. The most striking aspect of such a presentation is the approximately equal investment required for syngas production (ASU, AGR, and gasification) and for the conversion of the syngas into electricity. In a direct comparison with NGCC, this fact practically doubles the investment.

Typical investment costs for different types of new power plants have been sum­marized in Table 9-2.

These figures do not take any account of environmental performance, and the typical efficiencies do not reflect the maximum achieved by current IGCCs such as Buggenum (41.4%, HHV basis). The data does show, however, that with the expectation of increasing legislative pressure to reduce mercury emissions or capture C02, IGCC is better placed to respond than combustion technologies. These possibilities have been discussed in Section 7.3.

Availability and Reliability. As discussed, gasification is a capital-intensive process that provides a means of utilizing cheap and sometimes unpleasant feedstocks. It is therefore vital to the successful economics of a plant to ensure that it is operating at a high rate of utilization. This quickly becomes obvious when studying the figures in the examples above. An analysis will show that 1% higher availability (i. e., three days less per year off stream) is worth almost 3% increase in efficiency. It is also worth about 30% more than a 1% lower investment cost. These are facts of life for any capital-intensive production facility, and a consciousness of this is important at every level of decision making.

Gasification has not always had good press when it comes to issues of reliabil­ity. This is partly because still today, almost all plants are one-of-a-kind units that do not incorporate the benefits of standardization, and partly because the performance of demonstration plants has been more widely publicized than that of commercial operations. The technology is, however, also demanding in terms of operation and maintenance (О & M) know-how and understanding, and a fail­ure to recognize this at the inception of a project is a mistake that can be very costly in terms of downtime. On the other hand, there are many plants in different parts of the world that demonstrate that with the correct procedures in place, gasification can provide a reliability performance every bit as good as alternative technologies.

When discussing matters of reliability and availability, it is important to ensure that one is starting with comparable data. To assist in ensuring a common understanding, the Gasification Technologies Council has published a set of Guidelines for Reporting Operating Statistics for Gasification Facilities, based on the concepts of planned and unplanned outage and on-stream time. These guidelines are reproduced in Appendix D.

Data on commercial operation is limited, but Higman has reported on the operation of a number of liquid-feed plants (1994), including an example with a 98% on­stream factor. In another paper he reports on three Indian plants producing 110-123% of their annualized nameplate capacity (1998). Trapp (2001) reports an on-stream time of 97.8% for a coal-fed plant.

It should be recognized, however, that there is considerable difference in the performance of individual components depending on the feedstock. For resid burners, for instance, an inspection is required every 4000 hours with an antici­pated repair interval of 8000-12000 hours. Compare this with the 2200 hour life reported for a coal-feed injector (Trapp 2001). Although this difference is largely related to the difference in the abrasion characteristics of the feed, there are some indications that flashing of the water from a slurry-feed exacerbates this situation (U. S. Department of Energy 2002, p. 25).

Similarly, the very different ash in resids and coals (both quantity and quality) has an important effect on refractory life. Refractories in resid service require minor repairs at 16,000-hour intervals with a full replacement on a 20,000-40,000 hour cycle (Higman 1994), whereas in coal service uncooled “refractory liners are reported to last on the order of 6-18 months” (U. S. Department of Energy

2002, p. 26).

Given this background, it is essential for the success of any gasification project to recognize all the relevant factors and build them into the design and О & M strategies from the beginning. It is not possible in a book of this nature to develop a universal algorithm to finding the appropriate strategy for any future project. It is important, however, to give an idea of successful strategies and the philosophies behind them.

Number of Trains. For very large plants, there may be a minimum number of trains dictated by the capacity of the largest available reactors. With the steady increase in unit capacities that has been visible over the last 20 years, this is only likely to be a major issue for IGCC applications.

A second consideration is the behavior of the overall plant if one reactor is out of operation. If, as is for example in an ammonia plant, there are a considerable number of centrifugal compressors, then there is an incentive to maintain the overall plant operation close to or above the surge limit of the compressors. The strength of this incentive is, however, also dependant on a number of factors. With resid feed only the downtime due to burner changes needs to be planned in. This is usually a short operation, say 8 to 12 hours if the reactor reheat is considered, so the production and energy loss is relatively small in a two-reactor configuration, especially if they are configured as two 60%-capacity units.

In a coal feed but otherwise similar situation, where the reactor is also refractory lined, one would possibly need to consider relining a reactor in between major turn­arounds. This is an activity that can last as long as three weeks (again, including time for cooling down and reheating the reactor). This is intolerable, both because of loss of production as well as energy efficiency in a two reactor line-up. As a minimum, a spare offline reactor shell is required, which can be available and already lined prior to taking the operating reactor off stream. One can then simply swap the two reactors in the lined condition and restart, saving a considerable length of downtime. The lining repair can then be performed offline. We know of one plant that took this philosophy one step further and executed the drying out and part of the refractory preheating offline and swapped the (admittedly, relatively small) reactors hot, thus saving even more downtime. The implementation of such a strategy (whether the reactor swap takes place hot or cold) is, however, dependant on the layout and detail design of the facility, which must include access and other features to permit the quick removal of a reactor.

Spare Trains. In smaller plants, a strategy like the one outlined above may not be so appropriate. The saving in having two 50% or 60% versus two 100% capacity reactors decreases substantially with decreasing reactor size. Isolation of a reactor can only take place between relatively cold locations where valves can be used. This implies that, for example, a reactor including its syngas cooler has to be taken into account. Under such a situation, one can develop an operating strategy of keeping the spare reactor on hot standby and starting it prior to any planned refractory or feed injector repairs. This is the strategy employed by Eastman and is a key to their excellent reliability (Hrivnak 2001).

Operation and Maintenance. An additional key to achieving a high availability with a gasification plant is a high level of attention to detail in О & M activities (Hrivnak 2001).

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